Reply in a conversation
Posts a message to a conversation you already know the id of. Prefer POST /accounts/{account_id}/developer/messages, which accepts the same conversation id and additionally validates the messaging window and can address a contact or phone number.
Authentication
An API key created in Settings > Developer. A user token works too and is useful while you experiment. A key is authorized at the account level: it reaches every inbox, conversation and contact in the account that issued it, and nothing outside that account.
Path parameters
Request
Sends an approved WhatsApp template instead of a plain text message. Required to start a conversation, or to continue one whose 24 hour customer service window has closed. Supplying this field skips the messaging-window check on every channel, so only send it on a channel that supports templates.