Jobs at Djinni

We are looking for a detail-oriented and analytical PSP Manager to join our payments team and ensure seamless transaction flows across multiple markets. This role is essential to maintaining high conversion rates, troubleshooting issues, and optimizing the efficiency of our payment infrastructure.

Key Responsibilities:

• Manage relationships with connected payment service providers (PSPs) post-integration, including regular communication and issue resolution
• Analyze transaction reports, investigate failed or pending payments, and identify root causes
• Conduct ongoing monitoring of provider dashboards to compare performance data and spot discrepancies
• Evaluate payment conversion rates, interpret data, and identify key factors affecting performance
• Process internal tickets from business development and translate them into clear technical tasks for the integration team
• Liaise with new and existing PSPs to gather all necessary technical and operational documentation for onboarding and integration
• Perform competitive analysis of payment solutions across target regions (Africa, Asia, Latin America), identifying active PSPs, payment methods, and integration channels

Requirements:

• Solid understanding of payment conversion mechanics and experience working with conversion metrics
• Ability to analyze data and extract actionable insights to improve payment performance
• Experience working with PSPs and payment systems in the online gaming or iGaming industry
• Confident user of PSP admin panels and reporting interfaces
• Strong attention to detail and organizational skills
• Intermediate to Upper-Intermediate level of English (B1–B2) for communication with international partners
• Bonus: Familiarity with local payment methods and market specifics in Africa, Asia, and Latin America

What We Offer:

• Opportunity to work in a dynamic, fast-growing industry with a focus on emerging markets
• Collaborative team environment with cross-functional support
• Professional development and growth within a product-driven company

We’re looking for a fullstack developer who’s confident in both web and mobile app development. If you enjoy working with React, React Native, and Node.js - let’s talk! 
(At least 6 months of commercial experience)

Requirements: 
• Experience with JavaScript/TypeScript
• Hands-on experience with React (web) and React Native (mobile)
• Backend experience with Node.js (Express or Nest)
• Working knowledge of MongoDB or MySQL
• Understanding of REST APIs, authentication, and app architecture
• Basic experience with Docker
• Confident use of Git

Nice to have:
• Experience with Firebase or Supabase
• Familiarity with AWS (Lambda, EC2, S3, etc.)
• Debugging skills for cross-platform issues
• Understanding of CI/CD processes

Soft skills we value:
• Proactive mindset and ownership
• Clear communication
• Ability to work independently and in a team
• Attention to detail

What we offer
• Competitive salary
• Fully remote work
• Friendly and supportive team
• Paid vacation and sick leave
• Budget for learning and conferences

Interview process
HR interview → Test task → Tech interview + live coding → Offer

We’re looking for Flutter enthusiasts to join our team! Open to different experience levels, but commercial experience of at least 6 months is a must.

What you’ll need:
• Hands-on Flutter development
• Solid understanding of Dart
• Experience with third-party libraries and APIs
• Basic knowledge of mobile app lifecycle
• Awareness of UI/UX principles
• English: Upper-Intermediate or higher

Nice to have:
• Experience with Firebase or Supabase
• Backend experience with Node.js (Express or Nest)
• Familiarity with REST APIs
• Basic knowledge of Git
• Experience publishing apps to App Store / Play Market
• Work with payment services (e.g. Stripe, RevenueCat)

What you’ll do:
• Develop and maintain mobile apps with Flutter  
• Collaborate with the team on features and improvements
• Optimize performance and squash bugs
• Stay curious and keep learning

What we offer:
• Competitive salary
• Remote-first approach
• Friendly and open-minded team
• Paid vacation and sick leave
• Budget for learning and professional growth

Interview process
HR interview → Test task → Tech interview + live coding → Offer

You don’t just create beautiful videos — you craft creatives that convert.

You know it’s not about likes — it’s about results: clicks, engagement, retention.
If you can turn ideas into performance-driven ad creatives and use AI tools to do it faster and better — let’s talk.

We're hiring an AI-Driven Ad Creator —
In short: a full-cycle creative producer, from concept to final render.

Yes, with AI tools.
Not just someone who “played around with Midjourney,” but someone who uses AI as a real productivity booster.
Yes, with a performance mindset — you don’t make things that are just “pretty,” you make things that work.

What you’ll do:

• End-to-end production of mobile ad creatives — from brief to final export — solo.
• Use AI tools (Arcads, HeyGen, 11labs, etc.) to accelerate and scale content creation.
• Edit, animate, and finalize video & visuals for Meta, TikTok, YouTube, and more.
• Rapidly iterate and A/B test based on performance data and creative briefs.
• Maintain consistent quality, brand fit, and performance standards.

What we expect:

• A strong portfolio of ad creatives you’ve produced from scratch.
• Proven experience using AI tools (image/video generation, speech synthesis, character animation, etc.).
• Solid skills in video editing, motion design, and graphic design.
• Understanding of mobile marketing and performance creative testing.
• Excellent English communication skills (C1+).
• Willingness to complete a short test task.

What we offer:

• Competitive pay and flexible freelance collaboration.
• Fully remote, async work setup.
• Creative freedom to experiment with formats, tools, and ideas (Slack, Asana, Jira, paid AI tools).
• Official engagement via sole proprietorship / self-employed status + tax compensation.
• English required for daily work.
• A chance to work on high-impact campaigns for fast-growing digital products.

We’re looking for someone who knows how to make the most of FlutterFlow’s potential and isn’t afraid to dive into app logic, integrations, and clean UI.

Requirements:
• From 6 months of commercial experience with FlutterFlow
• Understanding of backend integrations and app structure
• Experience with Firebase or Supabase
• Basic logic building and data modeling skills
• Eye for UI/UX and responsive layouts
• General understanding of mobile app development flow

Nice to have:
• Experience publishing apps to App Store / Play Market
• Payment system integrations (e.g. Stripe, RevenueCat)
• Basic Git knowledge
• Familiarity with REST APIs

What you’ll do:
• Build, test, and maintain apps using FlutterFlow
• Connect UI with backend logic and databases
• Collaborate with the team on features and updates
• Continuously improve app performance and experience

What we offer:
• Supportive and easy-going team
• Fully remote work
• Fixed competitive salary
• Paid vacation and sick leave
• Learning budget and knowledge sharing

Interview process:
HR interview → Test task → Tech interview + live coding → Offer

• Responsibilities:
  Creating animations and video content for advertising campaigns
  Editing videos, adding graphics, working with sound and animation
  A huge plus is the ability to create deepfakes
   

• Requirements:
  Proficiency in After Effects, Premiere Pro, and/or other animation programs
  Skills in working with 2D/3D graphics
  Understanding the basics of design and editing/animation
  Creating deepfakes
  Creativity, attention to detail and the ability to work to tight deadlines

  Experience with Kreo in arbitration from six months

   

• Conditions:
  Work in a team of creative designers
  Probationary period: 2 months
  After passing the probationary period, it is possible to add KPIs
  Experience with creative and experience in arbitration/affiliate is welcome

We are looking for a strategic and hands-on Head of Marketing to take ownership of UKAD’s marketing strategy, positioning, and lead generation. You will be responsible for growing our visibility in target markets (Nordics, UK, US), supporting the sales team with compelling materials and campaigns, and aligning all marketing efforts with business goals.

 

Key Responsibilities

 

• Define and execute a marketing strategy aligned with UKAD’s growth objectives and regional focus.
• Develop positioning and messaging that reflect UKAD’s strengths in staff augmentation, .NET/Azure development, CMS migration, and AI solutions.
• Oversee performance of our website and ensure SEO best practices are followed (English + 4 localized versions).
• Lead and mentor a small marketing team (designer, content writer); manage planning, execution, and deliverables.
• Track, analyze, and report marketing performance metrics; recommend and implement improvements based on data.
• Build and optimize the content marketing funnel: service pages, blog posts, landing pages.
• Manage presence on Clutch and other review platforms; support case study creation and client success stories.
• Manage link building activities.
• Launch targeted social ad campaigns (LinkedIn, Google, Bing) and manage our LinkedIn presence.
  
   

Requirements

 

• 8+ years in B2B marketing, ideally in a software development, IT consulting, or SaaS environment
• Proven experience developing and executing international marketing strategies.
• Strong knowledge of SEO, paid media (LinkedIn, Google, Bing), and web analytics. Google Analytics certification or equivalent is a plus.
• Experience working with technical content and collaborating with developers. Experience in content writing.
• Strong writing and editing skills; able to produce clear, non-salesy content.
• Familiarity with SEO tools (e.g. Semrush).
• Strong management skills, including team oversight, goal setting, and performance tracking.
• Strong English
  
   

Nice to have: experience in lead generation and outbound sales support.

Our hiring process includes the following steps:

1. An initial introduction call with our recruiter team.
2. A practical test assignment to evaluate your skills.
3. A final interview with our C-level team.
4. Job offer.

What We Offer

 

• Opportunity to work remotely, or in a hybrid format.
• Flexible schedule – start your workday anytime between 08:00 and 11:00, whatever works best for you.
• Work equipment provided (if needed).
• Minimal bureaucracy – focus on work, not paperwork.
• Conferences, meetups – we support your professional growth
• Sane and polite, but effective management
• The best corporate culture (according to our teammates' opinions)
• Competitive salary and other stuff
• Becoming not just another developer, but a part of UKAD with unique value and long-term relationships.

Some facts about UKAD to help you make a decision:

 

- During 2022-2025, we only increased cooperation with our foreign partners.

- UKAD combines the benefits of family-sized companies, like no bureaucracy, easy access to the executives, with sustainable growth and vast opportunities.

- Our company is strong enough to be not just a vendor but a tech partner. We can afford to choose customers that respect developers.

- UKAD is one of the leading employers in Kharkiv, according to DOU.

.

Aren't we the company you're looking for?

RISK inc: An International iGaming Company Pushing the Boundaries of Entertainment
 

Who We Are:

An international iGaming company specializing in identifying and fostering the growth of high-potential entertainment markets. With 800+ professionals in 20+ locations, we operate in 10 countries, serving over 300,000 customers.
 

Always Pushing the Boundaries? You Already Belong at RISK!

Our global-scale operations are based on strong internal expertise, analytics, and data research. We have expertise in iGaming operations (sports betting, online casino), digital and affiliate marketing, tech solutions, and data analytics.

We are looking for an Middle Graphic Designer to join our team.

Qualifications

• Minimum 2 years of experience in iGaming / gambling / betting / entertainment industries Proficient in Photoshop, Illustrator, Figma
• Proven experience in creating: Marketing banners (web / mobile) Promo pages and landing pages UI graphics: icons, interface elements, pop-ups visuals for email campaigns, social media, push notifications
• Solid understanding of gaming aesthetics, UX specifics, and slot-style graphics
• Experience working with AI-based tools for visual content generation, enhancement, or editing (e.g. Midjourney, DALL·E, Runway, Firefly, etc.)
• A portfolio link is required, showcasing projects in iGaming or related industries We will evaluate: style, technical quality, logic behind design decisions, and ability to work with game aesthetics.

Responsibilities:

• Design high-impact marketing banners, for web and mobile platforms, tailored to iGaming and betting audiences. Create engaging promo pages and landing pages that support campaigns and drive user engagement.
• Design UI elements, including icons, interface components, and pop-ups aligned with modern gaming aesthetics and UX best practices.
• Develop visuals for multi-channel campaigns, including email marketing, social media posts, and push notifications.
• Maintain consistency in visual style, ensuring alignment with brand guidelines and the distinctive look of gaming and slot-style graphics.
• Utilize AI-based tools (e.g. Midjourney, DALL·E, Runway, Firefly) to generate, enhance, or edit visual content efficiently and creatively.
• Contribute to brainstorming sessions, sharing ideas for visual storytelling and campaign concepts. Iterate designs based on feedback, showing adaptability and a solution-oriented mindset.
• Ensure timely delivery of assets in a fast-paced, deadline-driven environment.

We offer: 

• Global Flexibility: Embrace the freedom to work from anywhere in the world, with remote work options that let you craft the perfect work-life balance.
• Vacation: 20 working days.
• Paid sick leave
• Learning Coverage 
• Team Building programs
• Mental Health Programs
• Sport coverage
• Medical insurance, dental coverage

Delasport — Implementing Technological Solutions Here and Now.

Delasport is an iGaming Software company providing Sports Betting & Online Casino software, and turnkey B2B solutions. Established in 2010, Delasport delivers a one-stop-shop solution of Sports Betting and Online Casino from a White-Label, with a full range of management services to a Plug&Play iFrame and a complete Turnkey. We are establishing an R&D center in Kyiv, and are looking for top talents to join our team.
 

RESPONSIBILITIES

• Gather required information/documents from various sources and evaluate the information for testing, provide meaningful feedback to Product Owners
• Actively participate in the team’s daily activities and Scrum ceremonies
• Plan testing activities together with the team in the scope of all release activities
• Determinate and estimate the testing scope on the different levels of SDLC
• Create and maintain detailed, comprehensive, and well-structured test cases and manage them in test suites
• Report and escalate release bugs and production incidents
• Create team documentation and keep up-to-date existing one
• Test and verify web applications (Sports Book) and APIs
• Use Postman for APIs testing
• Assist the development team with providing business- and technical-related information
• Operate Jenkins CI jobs/pipelines to build & deploy artifacts on designated environments
• Work closely with cross-functional teams, technology, and product managers, etc.

REQUIREMENTS

• At least 2 years of software testing experience
• Excellent level of theoretical knowledge in software testing
• Experience in API testing (Postman or similar tooling)
• Experience in analyzing the requirements, performing test design, executing test cases, and reporting test results
• Practical experience with testing web-based applications with API integrations
• Strong knowledge of stack of web technologies like HTTP, XML, JSON, REST
• Experience with bug tracking systems, as well as with bug reports creation and verification
• Experience and understanding Agile/Scrum methodologies
• Knowledge of SQL and NoSQL databases
• Upper-Intermediate English level

NICE TO HAVES

• Experience in Gambling testing

WHAT WE CAN OFFER YOU

• Modern office in Podil with an uninterruptible power supply and the Internet
• Personal time off (21 business days of paid vacation, paid days on special occasions, sick leaves, emergency days off)
• Public holidays
• Health insurance with the broker which is available from the first month of cooperation
• Life insurance with the broker which is available from the first month of cooperation
• Modern technical equipment
• English courses with native speakers
• Ukraine-based educational programs
• Sports activities reimbursement
• Corporate entertainments
• Happy hours on Fridays
• Gig contract support

About Us

We are a leading Israeli IT company with 15 years of market experience and 8 years in Ukraine. Officially registered in Ukraine, Israel, and Estonia, we employ over 100 professionals worldwide. Specializing in successful startup collaboration, we offer services across e-commerce, Fintech, logistics, and healthcare.
Our client is specialized in providing advanced data-driven solutions to the real estate industry. Our platform leverages cutting-edge technologies and analytics to deliver insights that help real estate professionals make informed decisions. We are committed to innovation, collaboration, and delivering impactful results. As a Senior Python Developer, you will play a pivotal role in shaping the future of our products and solutions.

Key Requirements:

🔹 7-9 years of experience with Python development, with a strong understanding of core Python concepts;
🔹 Strong problem-solving skills and the ability to write clean and efficient code;
🔹 Proficiency with Docker and Git;
🔹Strong problem-solving skills and the ability to write clean and efficient code;
🔹 Experience with PostgreSQL or other relational databases, and proficient in writing SQL queries;
🔹 Familiarity with cloud services (AWS or other cloud providers) is mandatory;
🔹 Strong understanding of workflow management tools (e.g., Airflow);
🔹 Experience with ETL tools and processes;
🔹 Strong experience working in Agile development environments with a focus on sprints and iterative progress;
🔹 English – Upper-Intermediate or higher.

Will be plus:

🔹 Experience with Pandas is a plus;
🔹 Geospatial data experience is a plus;
🔹 Familiarity with Flask;
🔹 Experience with machine learning/AI tools, models, or applications is a plus;
🔹 MLOps/AIOps experience is a plus.

What you will do:

🔹 Write high-quality, efficient, and maintainable Python code;
🔹 Design and develop scalable systems and applications with an emphasis on workflow management rather than backend processes;
🔹 Collaborate with product managers, business stakeholders, and cross-functional teams to understand requirements and deliver technical solutions;
🔹 Mentor junior developers and help improve their coding skills;
🔹 Work in an Agile environment, participating in sprint planning, standups, and retrospectives;
🔹 Troubleshoot and debug complex issues in a timely manner, ensuring systems are running smoothly;
🔹 Maintain and optimize the existing codebase, ensuring it is scalable and efficient.

Interview stages:

🔹 HR Interview;
🔹 Pro-Interview;
🔹 Technical Interview (Live Coding);
🔹 Final Interview;
🔹 References;
🔹 Offer.

Why Join Us?

🔹 Be part of a friendly international team, working together on interesting global projects;
🔹 Enjoy many chances to grow, learn from mentors, and work on projects that make a real difference;
🔹 Join a team that loves fresh ideas and supports creativity and new solutions;
🔹 Work closely with clients, building great communication skills and learning directly from their needs;
🔹 Thrive in a workplace that values your needs, offering flexibility and a good balance between work and life.

Hi there! 👋

We're seeking a talented graphic designer to help us shape the visual identity of an innovative educational app. Your designs will make learning engaging and intuitive for users. Experience with mobile app interfaces and a portfolio are required. 
 

Key skills: App UI/UX, creative visuals, user-focused design
Contract: Project-based / Freelance

We will have more tasks in case of smooth cooperation!

The company is an AI-driven drone and robotics firm specializing in advanced mapping, video processing, and hardware integration. Their goal is to develop intelligent, scalable backend solutions that power autonomous systems and automation.

Key Responsibilities:

• Design and develop scalable distributed backend systems for AI-powered drones and robotics applications.
• Build and optimize high-performance client-server architectures handling large volumes of data.
• Collaborate closely with AI, video, and hardware teams to ensure seamless integration.
• Ensure high availability, security, and performance of backend services.
• Take full ownership of tasks, from design to deployment, with minimal oversight.

General Requirements:

• 7+ years of experience as a backend engineer.
• Proven track record of delivering complex, high-performance backend systems.
• Strong problem-solving skills and ability to see the bigger picture beyond just code.
• Passion for technology and continuous improvement.
• Ability to take full responsibility for projects from design to deployment.
• Bonus: A degree in Computer Science, Mathematics, or a related field.

Technical Requirements:

• Experience with backend development in Python and/or Golang.
• Strong understanding of scalable distributed system architecture.
• Experience working with high-traffic client-server models and messaging protocols.
• Knowledge of system-level development, hardware integration, and security.
• Familiarity with:
  • Messaging & streaming technologies: MQTT, Redis, RabbitMQ
  • API development: REST
  • Databases: PostgreSQL
  • Containerization & orchestration: Docker, Kubernetes

Why Join?

• Work on cutting-edge AI and robotics projects in an exciting, fast-paced environment.
• Collaborate with top engineers, AI specialists, and product visionaries.
• Take ownership and play a key role in a growing company.
• Competitive salary and benefits package.

If you're a skilled backend engineer eager to tackle complex challenges and build next-generation AI-driven solutions, we'd love to hear from you!

Apply now and be part of the future of AI-powered robotics. 🚀

About Us
We are a leading Israeli IT company with 15 years of market experience and 8 years in Ukraine. Officially registered in Ukraine, Israel, and Estonia, we employ over 100 professionals worldwide. Specializing in successful startup collaboration, we offer services across e-commerce, Fintech, logistics, and healthcare.

Our client is an Israeli biotechnology company that develops AI-driven computational models of human diseases at the cellular level. By integrating vast amounts of proprietary and public data, their platform enables pharmaceutical companies to gain molecular-level insights, facilitating data-driven decisions throughout the drug development process. 

Key Requirements:
🔹 Relevant education or practical experience in Computer Science, Machine Learning, Mathematics, Statistics, or a related field;
🔹 3+ years of experience as a Software Engineer or AI/ML Engineer with a focus on building and deploying AI systems;
🔹 Hands-on experience with machine learning algorithms and statistical modeling;
🔹 Solid understanding of data processing, model training, and evaluation techniques;
🔹 Proficiency in version control systems such as Git;
🔹 Experience with both SQL and NoSQL databases;
🔹 Familiarity with cloud platforms (e.g., AWS, Google Cloud, Azure) for model training and deployment;
🔹 Basic knowledge of containerization tools like Docker and Kubernetes;
🔹 Understanding of scalable architectures and distributed computing for large datasets;
🔹 Proven experience working with cross-functional teams (data scientists, engineers, product managers);
🔹 Strong communication skills for articulating complex ideas to both technical and non-technical audiences;
🔹 English – Upper-Intermediate or higher.

Will be a plus:
🔹 Familiarity with MLOps tools and practices;
🔹 Experience deploying models into production environments and monitoring their performance;
🔹 Knowledge of optimization techniques for large-scale data pipelines;
🔹 Experience with workflow orchestration tools (e.g., Airflow, Prefect);
🔹 Background in deep learning frameworks and automated model tuning;
🔹 Strong communication and collaboration skills within multidisciplinary teams.

What you will do:
🔹 Participate in the design of scalable and maintainable software architectures for AI systems and data pipelines;
🔹 Take part in the development and optimization of high-scale pipelines and data infrastructure;
🔹 Contribute to technical decisions regarding tools, frameworks, and methodologies used in AI projects;
🔹 Help define technical roadmaps that align with business goals and innovation strategies;
🔹 Work closely with data scientists, ML engineers, and product managers to integrate models into complete AI workflows;
🔹 Provide mentorship and support to junior team members, promoting best practices and high-quality code standards.

Interview stages:
🔹 HR Interview;
🔹 Technical Interview;
🔹 Pro Interview;
🔹 Final Interview.

Why Join Us?
🔹 Be part of a friendly international team, working together on interesting global projects;
🔹 Enjoy many chances to grow, learn from mentors, and work on projects that make a real difference;
🔹 Join a team that loves fresh ideas and supports creativity and new solutions;
🔹 Work closely with clients, building great communication skills and learning directly from their needs;
🔹 Thrive in a workplace that values your needs, offering flexibility and a good balance between work and life.

 Responsibilities

• Project planning: setting clear goals, creating detailed timelines, and managing milestones and resources.
• Documentation: collecting client requirements, preparing briefs, and writing technical specifications.
• Team coordination: assigning tasks to creative, technical, and marketing teams, tracking progress and deadlines.
• Communication: acting as the main point of contact between the internal client (e.g., marketing team) and the project team, providing regular updates and reports.
• Risk management: identifying potential issues, developing preventive strategies, and adapting plans when needed.
• Quality control: ensuring the final output meets client expectations and internal quality standards, including testing with QA.

 Requirements

• 1+ year of experience as a Project Manager in digital or marketing projects.
• Strong planning and multitasking skills, with the ability to manage documentation and timelines.
• Solid understanding of workflows across creative, tech, and marketing teams.
• Excellent communication skills: confident in presenting ideas and managing expectations.
• Experience in client communication, conducting negotiations, and adapting project scopes.
• Problem-solving mindset with the ability to identify and mitigate risks under pressure.

 What we offer

• Competitive salary and performance-based bonuses.
• A chance to work with a dynamic team in a fast-growing industry.
• Exciting challenges and real opportunities for growth and career advancement.
• A fun, vibrant work environment with team events and perks.
• Opportunities to attend professional events, trainings, and conferences.

We’re seeking a seasoned DevOps Engineer, who will join a team responsible for managing our client's cloud infrastructure, ML tools, and monitoring systems.

The role implies overseeing day-to-day operations, improving existing processes, and contributing to building new solutions.

If you're passionate about building top-tier desktop apps using cutting-edge technologies, we’d love to hear from you! 

CUSTOMER

Our client is a rapidly growing technology leader in digital accessibility software that helps enterprises make their web and mobile offerings accessible to everyone. Its AI-enabled products save developer time and reduce risk via proprietary discovery and analysis algorithms that integrate directly into software development pipelines.

Resposobilities:

• Design solutions and improve our product architecture
• Plan and execute complex, diverse, large-scale software delivery systems
• Research and integrate new technologies into our stack.
• Monitor and implement ways to improve the efficiency and cost-effectiveness of our solutions

Qualifications

• At least 4 years of hands-on experience in a modern SaaS environment (AWS/GCP/Azure)
• Experience with Infrastructure as code (IaC)
• Experience with CI/CD methodologies, using relevant tools (e.g., CircleCI, GitHub Actions)
• Strong expertise in Docker, Kubernetes and Helm
• Proven experience managing live production environments, including monitoring and alerting
• Proven experience working with production environments.
• English - at least Upper-Intermediate level

WILL BE A PLUS:

• Experience with data lakes and MLOps
• Experience with NoSQL and Big Data databases (e.g., Elasticsearch)
• Background in networking, security, and compliance

Additional information:

• Independent, autodidact, excellent problem solver and passionate about learning new stuff
• Great communicator and collaborator with a total commitment to providing the best services to all stakeholders