Hi there!

Sorry for your issue.

I have just tried your form here: http://luxyort.10gaarden.dk/index.php/da/faq/kontakt and it is working fine here at my end, showing success message. Has your issue already been solved?

However, The following tip may help:

https://www.joomshaper.com/documentation/sp-page-builder/sp-page-builder-3/troubleshooting#prohibited-input-u-00000020-when-submitting-a-form

Best Regards