In order for Google Ads to allow CTM to send offline conversions auto-tagging must be enabled.
1) Sign in to your Ads account.
2) In the left page menu, click Settings.
3) Click Account settings along the top of the page.
4) Click the Auto-tagging section.
5) To enable auto-tagging, check the box next to “Tag the URL that people click through from my ad.”
6) Click Save.