Google sometimes does not accept a tracking number as a call extension, for example.

1. What can I do to be able to use the individual telephone number as a call extension?

a) Please do not register the phone number in +49711 xxx format, but with the leading 0 (e.g. 0711 xxx). This is sufficient in many cases.

b) Use a meta tag. The corresponding tag could look like this. This means that this telephone number is also stored on the website:

c) Create a hidden div container that is saved on the web page and contains the telephone number that will be used as a call extension.
This means that the telephone number can now also be found on the website.

2. What do I do if nothing works?

In such cases, we advise you to contact Google Support directly, indicating for which of the reasons given below the telephone number has been rejected.
https://support.google.com/adspolicy/answer/6368661?hl=de#678