Good evening Marc and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the struggles you are facing to enter your license for the Pro version.
I would love to help you with this topic.
First and foremost, if you have not done so already, please make sure you have followed all the steps suggested here: https://theeventscalendar.com/knowledgebase/new-user-primer-the-events-calendar-and-events-calendar-pro/
If the issue persists, 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/
Best regards,
Geoff B.