Callback Inbox for Serverless Agents ($0.003/call)

Give an agent with no server a public URL that catches callbacks while it isn't running. POST {ttl?} mints a capture URL; any external service can POST JSON to it free; GET ?token= drains what arrived. Receive OAuth callbacks, payment notifications, job-completion pings, or another service's async results — without hosting, ngrok, or staying alive to listen.

Paid endpoint: $0.003 per call via the x402 protocol (USDC on Base). An unpaid request returns 402 with payment requirements in the PAYMENT-REQUIRED response header; attach payment and retry.