Start a channel thread
Send the opening message on channel and bind the recipient’s phone
number to a conversation thread. The agent is identified by your access
token. Omit thread_id to start a new thread (its id is returned); pass
it to continue an existing one. Template fields apply to WhatsApp only.
Authorizations
Access token from POST /management/v1/auth/token (publishable-key exchange) or a login session. Publishable-key tokens are agent-scoped and serve the messaging surface; login tokens also serve management.
Path Parameters
Channel id: 'whatsapp' or 'sms'.
Body
Start (or continue) an outbound-first thread on a channel — the agent is
identified by your access token. thread_id is optional: present ->
continue that thread; absent -> a new thread is created and its id returned.
Recipient phone number in E.164 (e.g. +14155551234).
When set, continue this thread instead of creating a new one.
^[0-9a-fA-F]{24}$User id for a new thread; defaults to the phone's digits.
Opener body for non-template channels (SMS). Ignored by WhatsApp (uses templates).
WhatsApp only: bound to template variable {{1}}.
Optional sender to send from (your connected number). Omit to use the platform default sender.
Optional runtime build pin (e.g. '0.5.4') for agents on the runtime-v2 engine. Has no effect on which engine serves the agent; omit to use the current default runtime.