[plugin: All In One Event Calendar] add custom field (v 1.10.9)

Hi all,

Via a custom made script people are able to subscribe to events created with the All In One Event Calendar (ai1ec) plugin with one click on a button. The button only shows up when in the database table ‘wp_ai1ec_event’ column ‘subscribe’ is set to 1. It’s all working.

But now I would like to add a custom field, a checkbox, to the create events window. I have been able to find how this should be done for older versions, but the line numbers don’t match and I could not figure out the new lines.

Could someone please explain how to add a custom field (checkbox) to the ‘add events window’ at the backend of wordpress/ai1ec? Is it possible to make this version independent?

Kind regards,
Cor