Hi there Barback,
Thanks for getting in touch with us!
I was reviewing this and found a known bug affecting the form and outputting an error message in the tickets form (in the event list or in the single event screen). The fix for this issue will be released in the next maintenance release (4.3.5) coming out next week (if everything goes as planned).
If you can wait for the update I can try to downgrade the plugins and see where this started, hence find a ‘safe’ version of Event Tickets Plus to use for now.
Please let me know about it,
Best,
Nico