Waste of time. Does nothing …

How do you know that the error wasn’t yours? Why didn’t you try to contact the plugin’s author about this by posting a topic in the plugin’s support forum?

Try reviewing:
https://pippinsplugins.com/how-to-leave-a-good-bad-review/
https://chrislema.com/theres-wrong-way-give-plugin-feedback-wordpress-org/

Hi,

By reading your issues, it seems you didn’t install the plugin “CMB2”, it should be displayed as Required when you install Modal Popup.

CMB2 handle all the editor part, that’s why I think it must be the solution.

If you are still wanting to use the plugin, we would be glad to help you to implement it.

Best Regards,
PluginlySpeaking