One API, every channel

Use the same message resource across SMS, MMS and connected channels. Put the message body or media in content, select channel behavior with channel_options, and inspect warnings before treating a request as complete. Use contact_id when the recipient is already known.

Discover supported channel types with GET /v1/channels/types. Scope API keys to the account, lines and actions they need, and keep send and read keys separate. A channel may add warnings or hold reasons without changing the message contract.