Plexamp not working

Here is my issue. I have music on my music media server and am having issues with Plexamp. Now playing music via the app on PC in browser works fine. However when I open the app on my phone (IOS) it asks me to sign in and I get internal server error. Dealeted and re-loaded app but still same issue. So downloaded the desktop plexamp app (Microsoft) and same issue. Checke the username and password and that is correct. Help please.