502 Bad Gateway when trying to login as a user

Hi, I am trying to configure keycloak using saml to have a SSO for https://credentials-test.hedup.com/
It works if I click on the saml login but if I enter my user credentials I get 502 Bad Gateway.

Some more info is provided in the screenshot, sorry if it is a bit messy but as a new user I can only add one screenshot.
I am wondering if I have configured it wrongly to get an invalid xml file which I have to enter in the app I am trying to connect. I have created admin and user roles plus given my user access to both. I am completely new to keycloak and have spent a lot of time trying to connect as a user so any advice would be amazing. I hope I have provided enough information and please let me know if I am missing something. Thanks!

I made some updates which can be seen here: