Limits

JSON request bodies are capped at 64 KiB. Larger bodies are rejected rather than truncated. Media uploads have kind-specific ceilings documented on the upload operation.

Paging inputs are refused rather than clamped. Send a supported limit and preserve returned cursors exactly.

Each API key has a request rate limit and a cap on open event streams. Going over returns HTTP 429 with error.code 4012 or 4013 and a Retry-After header. Wait that long and retry, and close event streams you don’t use.

Handle HTTP 429 on every operation. It carries a registered numeric error.code and, wherever a retry time is honest, a Retry-After header mirrored by error.retry_after. What the wait means depends on the code — for 4006 (a spend cap) it is the exact reset of the cap window; for 4008 (the distinct-customer ceiling below) it is a minimum, and a retry then may still be refused. See error handling.

The channel’s portfolio-level messaging tier is separate from this API’s request rate. The phone-number read exposes the reported tier token but does not publish a numeric ceiling in this version.