Backend Engineer for Meta Messaging Integration

We are looking for an experienced backend engineer to help River migrate our messaging integration from Unipile to direct Meta APIs.

The project involves integrating directly with Meta's messaging products, including Instagram Messaging, Facebook Messenger, and WhatsApp Cloud API. The goal is to support account connection, incoming message webhooks, outbound replies, message status updates, attachments/media, and reliable error handling.

You should have strong experience with:
- Meta Graph API
- Instagram Messaging API
- Facebook Messenger Platform
- WhatsApp Cloud API
- Webhooks and event processing
- OAuth and token management
- Python backend development
- Async APIs, Pydantic, and FastAPI-style services
- PostgreSQL or Supabase
- Google Cloud, Pub/Sub, Cloud Functions, or similar infrastructure
- Meta platform policies, app permissions, and webhook security

Responsibilities:
- Implement direct Meta account connection flows
- Receive and verify Meta webhooks
- Normalize incoming messages into our existing inbox system
- Send outbound messages through Meta APIs
- Support media and attachments
- Handle reconnects, token expiration, retries, rate limits, and provider errors
- Add tests and staging validation for the integration
- Help River safely migrate away from the current Unipile-based integration

Nice to have:
- Experience with Meta App Review
- Experience with WhatsApp message templates
- Experience migrating from a third-party messaging aggregator
- Experience working with CRM, inbox, or customer messaging products

Policy compliance:
- You understand Meta's usage policies around outreach, follow-ups, templates, consent, and other message types.

Please apply with examples of previous Meta, WhatsApp, Instagram, Messenger, or webhook-based integrations you have built.

We are looking for someone who can own the integration end-to-end, communicate clearly, and work carefully inside an existing production codebase.