Azure app proxy question

Hi,

I have an interesting App Proxy question. I am trying to connect to an o prem application. I have setup enterprise app connected to app proxy. However I am unable to log into the system, I get a 404 error and I am trying to identify how to fix it.

dns=system.domain.com/applicationname

The url is https://system.domain.com/applicationname

I can see this gets redirected to https://sytem.domain.com/applicationname-login/Security/Login?redirect=http2F%2Fsystem%2F%3blarblar%3 and login fails.

The error is no webpage was found for the web address.

https://sytem.domain.com/applicationname-login/Security/Login?redirect=httpF%2Fsystem%2F%3blarblar%3

However if I use one of the other functions and update dns to system.domain.com/applicationname-login/security I am able to get to and log into this part of the application (the url does not redirect).

I can log into the application from the app proxy server (server 2019) without any problems.

Struggling where to start troubleshooting this as there is nothing in the logs on app proxy server nor on the application server. It is getting past Azure authentication I think.

Any suggestions gratefully accepted