Option to add or edit fields not functioning

Hello,

Since we put the website on a live location the plug-in isnt functioning like it should.
The option to edit or post an field group will result in a 500 error on the back-end side of the website.
Note: The options are functioning perfectly.

We tried the following things:
– Added a new .htacces file
– Updated the plug-in to the latest version
– Reuploaded the WordPress core files
– Turned off every plug-in to see if there were any conflicts

None of the above resolved the issue, hopefully you can help us to find the source of this problem.

Regards