When adding Liine tracking numbers as 'Google Ad Call Extensions/Assets', these can be 'Disapproved' by Google since they cannot locate our tracking number on your website/landing page.
Here are the two ways we have seen teams resolve this 'Number Verification' situation with Google Ads Call Extensions:
Google has an option to link your Google Ads account with Search Console. With this method, you have to verify your domain through the search console, but once it's integrated - you can resubmit the number for review & it should successfully go through from there.
Have the phone number added directly to the website/landing page somewhere. For example, we have seen teams add our tracking number to the footer, with the number set as the same footer color to blend in so it was hidden.