I've gotten 3rd party free SIP clients working. Typically, I use traceSM in Session Manager to watch the register messages from an Avaya phone and compare/contrast with the 3rd party client.
To be honest, all you need is the Session Manager traffic IP (not the management IP), the username, the SIP domain, and the Communication Profile Password. Its just a guessing game of where you might need to put those things. Is your user 1234? Or 1234@yourdomain.com? Maybe user is 1234 and authID is 1234@yourdomain.com?
traceSM will at least let you see where in that app's setup that those values truly get into a register message.