Unfortunately our whole back and forth was really un-helpful. I don’t like the way the client’s original developer created this site, but changing the theme isn’t really an option. Also I am NOT a theme developer so I have no clue how to use that error screenshot to troubleshoot. Do you have any other ideas I can try to get this to work, or do you have any suggestions on a developer to pay to take a look and fix the integration? Trying to avoid having to find a different calendar for them since they really like yours otherwise.
Unfortunately I do not have access to the theme developers, and I do not develop themes, or use custom post types the way they did so I am lost with trying to troubleshoot this.