Hello @klaasfeuth,
Thanks for writing to us.
It seems that there might be an issue with the permalink. Please note our builder uses the rest API. The WordPress Rest API only works properly if the permalink is set as “Post Name”.
I would suggest you set the permalink as “Post Name”. If the site is not working when you are setting the permalink as “Post name “, it might be the issue of the”.htaccess " file. It might be the”.htaccess " file corrupted or it might be the issue of file permission. The “.htaccess” file is located at the root directory of the WordPress installation.
Please have a look at this article https://wordpress.org/support/article/htaccess/
In case if it is not working for you please contact your hosting provider to fix the permalink issue.
Thanks