Getting 404

Hi, I’ve set up the custom thank you page and the plugin. However I’m getting a 404 error. I also have WPML activated, maybe this is the problem? Before purchasing and getting WPML support, I wanted to see the plugin work. Here you can see the problem yourself: https://jumpshare.com/s/Yo6gWLqNzR5MR4uE0Efg

thank you for help, Frank