Referenced AMP URL is not an AMP

Google search console is throwing up Referenced AMP URL is not an AMP for a lot of my URLs.

I checked the amp validator tool and the test fails as well. The errors are a lot but the number error is “The mandatory attribute ‘?’ is missing in tag ‘html’.”

There seems to be an issue with either my AMPforWP settings or my theme. I’m not sure which.

Would be grateful for any help as this is frustrating and is beginning to affect my rankings.

example URL: https://koboline.com.ng/how-to-block-gtb-account-online-with-code-from-another-phone/.

Thank you.