The call flow
1
The customer calls
The customer taps the call button in the chat with your WhatsApp Business number.
The button is shown on iPhone and Android. Calls from WhatsApp on the web or desktop are not supported
by Meta.
2
Meta sends the call to OneXtel
Meta places the call to the OneXtel gateway over SIP on TLS. The gateway asks Meta to authenticate
with the credentials generated for your number, and accepts only calls that authenticate and that come from Meta’s networks.
3
The gateway finds your trunk
Each WhatsApp number is linked to one or more SIP trunks that you provided. The gateway tries them
in priority order, and moves to the next if one does not answer in time.
4
Your platform answers
Your voice platform receives a normal SIP INVITE and answers it. The caller’s WhatsApp number is
carried in the SIP From header, and your WhatsApp Business number in the request address.
5
Audio flows both ways
The gateway carries the audio between Meta and your platform. WhatsApp uses encrypted audio with
the Opus codec. If your platform prefers G.711, the gateway converts between the two.
6
The call ends
Either side hangs up, and the gateway closes the call on both legs and records the result.
Number states
A WhatsApp number moves through these stages during onboarding. You see them in the call record and in conversations with your account team.
Calls to a number that is not configured are refused.