Rest API Server: Voice AI Agent Development

We're building an internal API server that sits between our white-label reseller clients and a third-party voice AI provider. When a reseller calls our API, the server provisions AI voice agents on their behalf, manages SIP phone number bindings, handles knowledge base content, and fires webhooks back to the reseller.

Full technical specifications will be provided — this includes a complete database schema, endpoint-by-endpoint business logic, provider integration details, webhook event schemas, and a monthly billing automation flow using Stripe.

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WHAT NEEDS TO BE BUILT
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1. API server (Node.js, Python, or Go — your choice)
- JWT/bearer token authentication with SHA-256 hashed API keys
- Full CRUD for Deployments, Agents, SIP Identifiers, and Knowledge Sources
- All endpoints follow the spec provided (request/response shapes are fully defined)

2. PostgreSQL database (Supabase)
- 7-table schema (provided in full): accounts, deployments, agents, sip_identifiers, knowledge_sources, billing_periods, billing_line_items
- Multi-tenant with row-level scoping by account_id
- AES-256 encryption for sensitive fields (API keys, SIP passwords)

3. Voice AI provider integration
- Isolated service layer for agent creation, updates, deletion
- Knowledge base pass-through
- SIP identifier registration
- Inbound webhook receiver from the provider → translate and forward to client

4. Outbound webhook system
- HMAC-SHA256 signed webhook dispatch to client URLs
- Exponential backoff retry (5 attempts)
- Events: deployment lifecycle + call transcripts

5. Monthly billing automation
- Cron job (1st of month) queries provider for per-agent call minutes
- Aggregates by deployment and account
- Creates Stripe Invoice with line items
- Generates branded PDF invoice
- Emails client via SendGrid / Resend

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WHAT YOU'LL RECEIVE
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- Complete database schema (all columns, types, constraints, indexes)
- Full endpoint specs (request body, response shape, internal SQL, error codes)
- Provider integration guide (what to call and when)
- Webhook event map and signing spec
- Billing flow walkthrough with SQL queries
- Security checklist

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REQUIREMENTS
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- Strong experience building REST APIs in Node.js, Python, or Go
- PostgreSQL / Supabase experience
- Stripe API experience (Invoices, Customer Portal)
- Clean, commented, production-ready code
- Must be completable within 1–2 weeks

Please include examples of similar API server projects in your proposal.

NDA required before full spec documents are shared.