HAProxy with basic auth 500 Internal Server Error

[cougarmaster]

I have HAProxy setup for a few dockers and all are working no issues. The one I am having problem with is a docker which is connected on the backend with basic auth and show connection on the frontend ok.

Then when I connect to it and entering the username and password it show :-

I have the same thing running on several other installation on different locations and they all work without problems. What am I missing? If I access the docker locally it works.