Good afternoon Dimitri and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the error 500 message you have been experiencing while using RSVP tickets.
I would love to help you with this topic.
As a first troubleshooting step, could you please provide us with your complete system information in a private reply using the instructions found in the following link?
https://theeventscalendar.com/knowledgebase/sharing-sys-info/
Secondly, Could you send me a screenshot of your edit ticket button ?
Finally, can you tell me if you changed the tickets type from WooCommerce to RSVP?
Best regards,
Geoff B.