I can confirm this is still an issue on the website today. The app does work fine, though. Called support before using the app and they just said to wait an hour or try at the airport so they seemed clueless to the bug.

Best to just use the app.

Once you check-in on the app you can email yourself the ticket information and print it out if you prefer to use paper over the app.

To help people find this post easier here is the exact error I get on the AeroMexico website "Please make sure you've entered an accurate number"