Good evening Kathrine and welcome back!
First off, I would like to apologize for the delay answering.
We are currently experiencing a higher level of requests than usual.
Please rest assured that we are working hard at correcting this situation.
We appreciate your patience while we try to normalize things.
Thank you for reaching out to us.
We are sorry to hear about the internal server error creeping up on your site while customers are going through their checkout. I would love to help you with this topic.
I believe this is a side effect of the recent WooCommerce 3 upgrade.
This upgrade included some major changes that created several issues with various plugins, including ours.
The good news is that we were quick to release a fix for these issues.
Upgrading Event Tickets Plus to 4.4.5 should fix this for you.
Let me know how that goes.
Best regards,
Geoff B.