Call2Teams - Customers
When entering phone numbers against a user, the error "The telephone number provided is not valid " is seen:
This is because the number should be in E.164 format, in order to be mapped to Microsoft Teams.
E.164 is the international telephone number format: [+][Country code][Subscriber number]
Ensure the phone number entered is in a compatible format.
See this article for more information about E.164 format: