Stay log in an app

I have Suddenlink as my cable provider and Starz is in my package.

I use an Apple TV+(latest gen) for streaming.

I downloaded Starz App and logged in using Suddenlink as TV provider.

I can watch the Starz App once, maybe twice at the most, once in awhile and then Starz App wants me to login again.

I have to go the settings, system, restart and then go on my iPhone to activate.com/Starz, then open the Starz App and click on login. Then Starz App opens and gives me a 4 letter/number combo that I have to enter on my iPhone and then the Starz App actives and opens and then I can select the show that I want to watch and it will start.

Why do I have to continually have to do this? Why can’t the Starz App stay logged in?

I watch Outlander the most.