WHY IS APPLE LETTING SAFARI TO GET HIJACKED BY CHROME?

Not familiar with the Government site "MY PAY", but I do use Safari to manage by Chase banking account with no problems. Some things to check are some sites require Pop-Up Windows which are blocked by default on Safari and you may need to allow them for that site. Also, check for Extensions in Safari including Ad Blockers or Pop Up blockers that could be preventing the site from continuing. Here are some other solutions for Safari not working with web sites:

If Safari won't open a page or work as expected on your Mac – Apple Support (AU)

Does the same thing happen when starting up in Safe Mode?

Use safe mode on your Mac - Apple Support

If you are still unable to access the sites needed and have tried other users suggestions, then that just leaves contacting Safari Support here:

Safari - Official Apple Support

If a website chooses not to support Safari, there is nothing Apple can do about it (other than rewrite Safari). That being said, I can log into my Chase credit card account with Safari.

Forum tip: Don't type all in caps. It's very hard to read and is considered shouting. Some people will not even bother to read a post typed in caps.