Do not disturb or flight mode is switched on
You want to register an existing number with the WhatsApp Business API, but you are in a meeting marathon and have therefore set your mobile phone to silent mode or even flight mode two hours ago? This may be the reason why Facebook can't reach you and there is no verification call. So check your settings on your mobile phone and adjust accordingly 📱
Voicemail / Answering machine / On hold
The number you want to register on the WhatsApp Business API or the call forwarding you have set up in Superchat which you want to use to receive the verification code, is your central number which leads to an answering machine or instantly puts the caller on hold.
Because the verification call is an automated one, the tech behind it cannot always distinguish between an answering machine and a real person on the other end. In most cases, if there is an answering machine, the call will be disconnected immediately, or the call will end before the announcement or answering machine ends. So, turn off the greeting, queue or answering machine for a moment until you receive the call from Facebook.
Alternatively, you can divert incoming calls for a moment to bypass the greeting, queue or answering machine.
💡 Hint: The best way to test this is to make a call from your private phone to the number in question. If you get through directly, you're good to go!
0800 number(s)
In case you are in the process of registering an existing 0800 number with the WhatsApp Business API, the verification call from Facebook will also be sent to this number. In this case, the call comes from an English number. German freecall numbers with 0800 prefixes cannot be reached from abroad in most cases.
So make sure that the number is an internationally valid one. If you are unsure, it is best to contact your provider and ask them.
(The same applies if you want to register a Superchat number with the WhatsApp Business API and have stored a 0800 number as call forwarding in Superchat.)