WHMCS and our plugin attempt to format your input in such a way that it can be used by our API and other external systems. Sometimes this conflicts with your usual way of working.

131- Invalid telephone country code!

The most common cause of a phone number being judged as invalid is because users leave the phone number field empty, however this is a mandatory field in Openprovider. 
Another common cause of this error is when users add a country code to the number. WHMCS does this as well (using the country of the contact to get the country code) and this results in +3131 making it an invalid country code.

Solution: Review the phone number of domain contacts and add/correct it.

133 - Invalid telephone region code number!

Area/region code is part of the phone number (excluding leading zero). Incomplete phone number or invalid format in phone number can cause this error.

Solution: Review the phone number of domain contacts and correct it. If you have the following option disabled in WHMCS Admin Dashboard > Configuration > System Settings > General Settings > Localisation (tab), specify the phone number in a format like +XXX.XXXXXXX having dot (.) symbol included as a delimiter.

By default, WHMCS uses the following phone number format, automatically prefixing the number with the international country dialing code for the client’s selected country:

+ [Country Code] . [Phone Number]

135 - Invalid telephone subscribers number!

Incomplete phone number, invalid format or invalid characters in phone number can cause this error.

Solution: Review the phone number of domain contacts and correct it.

If the cause is not clear, feel free to contact our support department. They can check the logs and see what is being sent to the API and possibly hint you in the right direction.