Send a message

Text, an approved template, buttons / a list, or a file (mediaId) on a connection, to a thread, a contact or a new recipient. 201 when the channel sent it now; 202 with status: queued when it is dispatched in the background (watch message.status_updated). Outside WhatsApp’s 24-hour window only a template may be sent (422 unsupported_channel_action, reason outside_24h_window). On WhatsApp Cloud a template sent with to or contactId starts the conversation (contact and thread created or reused); free text to someone with no conversation is 422 outside_24h_window. A template must be approved, in the given language and given exactly its variables (422, reason template_not_approved / template_language_not_found / template_variable_mismatch). A template with a header or buttons takes template.header (text, image, video, document or location; media by mediaId or a public https link) and template.buttons (by index: quick reply payload, dynamic URL suffix text, copy code text, flow payload), checked against the template (422, reason template_header_required / template_header_mismatch / template_button_not_found / template_button_mismatch / template_button_parameter_required). WhatsApp Web numbers have warm-up caps (429, reason whatsapp_web_daily_cap / whatsapp_web_minute_cap) and every response carries warnings: ["whatsapp_web_unofficial"]. The Idempotency-Key also de-duplicates the send itself, beyond the 24-hour replay window.