Gateway over the WhatsApp Cloud API POST /{phone-number-id}/messages endpoint.

Send the exact same JSON body you would send to Meta — text, media, location, contacts,
interactive, reaction and mark-as-read payloads are all supported — but authenticate with
your WAX bearer token instead of a Meta access token. WAX forwards Meta's response
(success or error) verbatim, so existing Cloud API clients keep working unchanged.

Template messages are not supported: use WAX campaigns or flows instead.

POST /v1/whatsapp/messages sends through your default WhatsApp phone number.
POST /v1/whatsapp/{phone_number_id}/messages (Meta phone number id) targets a specific number.