1031: Idempotency-Key header is required on all sends; it makes blind retries safe

Idempotency-Key header is required on all sends; it makes blind retries safe. This is an HTTP 400: the request could not be parsed.

• Check this endpoint’s request schema in the API reference; param in the response names the exact field at fault.
• Use an official SDK, which enforces required fields and types before the call is made.

• Sending a message