Hi @marcorm69,
Usually the form freezing on changing of the payment gateway is related to something blocking access to a specific file called admin-ajax.php. That file is necessary for GiveWP to switch the payment method.
One commone reason that file is blocked is if sites load over both http and https.
A security feature of that file is that it is not able to be executed from a different url. https://example.com and https://example.com are technically different URLs. So if a person is visiting in a browser that is on https://example.com and attempting to execute the file at https://example.com the security feature kicks in and prevents anything from happening.
The fix is to route all traffic on your site to https, and to change all instances of the http version of the URL in the database to the https version. Another “gotcha” that sometimes results in frustration is that the www and non-www versions all need to be standardized, and the files should be delivered over the same version (https://www.example.com or https://example.com) that all traffic is forced over.
We have a detailed tutorial that covers these items really well. The article will walk you through the following things that are relevant to this issue:
1. the “update your Site URL” section
2. the “Force HTTPS Throughout your Site” section
3. the “Resolve insecure elements your Pages” section.
That article is here: https://givewp.com/documentation/resources/how-to-use-ssl-and-https-for-your-wordpress-website/
Let me know if you need further assistance. Thanks for using GiveWP! Have a great day.