Hey Dennis.
Here’s the error in the console.
The first factor to look at is that CORS issue. That is connected to the server or web hosting setup. Please try contacting your web host for this to enable CORS. This article might help you understand: https://enable-cors.org/
Since it is a live site, we cannot test for a plugin conflict. You will need to do the plugin conflict. You’ll need to do the plugin conflict test yourself. In case you don’t know, you can do this by deactivating all third-party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time. But, it’s best to do that in a staging copy of your site. Here’s a guide to set up a staging copy of you site: https://www.wpbeginner.com/wp-tutorials/how-to-create-staging-environment-for-a-wordpress-site/
Thanks for testing.