Google offers forwarding numbers for your call-only ads and call extensions.
These forwarding numbers are used to track calls inside of Google Ads. More about Google Forwarding Numbers.
For CTM to track calls from your call-only and call extensions, you’ll need to place your CTM tracking number as the phone number for call-only and call extensions.
If you would like CTM to capture the Campaign, AdGroup and Keyword for your call only and call extensions, you’ll need to create a double forward. Meaning, that you’ll have a Google Forwarding number forward to a CTM Tracking number. The dual forward will allow both systems to track the call. If both methods aren’t tracking the call, the campaign, ad group, and keyword data will not report in both systems.