Starz streaming problem

I am paying for a premium package that includes Starz, HBO, etc.  I am using an Amazon Firestick on three TV's and have all of the apps for the premium channels that I pay for and they all recognize my account except STARZ.  When I try to log in using my Direct TV streaming account info I get an Authentication Error, which goes on to say that I am not authorized for Starz service.  I just (again) went to check my account which does include Starz. Please advise!