I just cancelled my Amazon Music HDUltra less than 3 hours into the trial. Even if the above problem was fixed, get a load of this: there is no way to find a song or playlist on your phone and cast it to your Firestick. But you can cast it to a chromecast.

This BTW is completely contrary to how Amazon Prime Video works.

Completely unusable for me.

Proprietor - House of the Rising Sone