I have problems with Westpac and Firefox. One routine operation always gets an incorrect error from them that they are having technical difficulties. The second time click always works. I have numerous other web sites that work, partly work, and sort of work with different browsers.
A normal reply is to clear your browser cache and cookies. Sometimes it actually works and sometimes not.
Suggest you try a different browser to see if yours might be part of the problem (browser, its cache or its cookies). The popular ones include chrome, firefox, opera, internet explorer and edge, and a few others that are relatively obscure.
I also have a media site I frequent and neither chrome nor firefox properly handles the automated login and just returns 'unexpected error' when I try to post something. Opera gets it right, while some web sites complain about opera being old and I need to upgrade to a new one. The internet is what it is.
I hope this might have helped.