I pay for Showtime thru my cable provider Spectrum. How do I get the TV app to recognizer that?

The Apple TV app Channel Showtime is a different subscription from Showtime using a separate app (iPhone, iPad, Apple TV box), or on the web (Mac). These subscriptions are not exchangeable, as they have different Terms & Conditions, and different perks.

Apple TV Channels FAQ: Services, pricing, availability, and everything else you need to know - Macworld

Subscribe to Apple TV channels in the Apple TV app - Apple Support

Hello,

You will need to reach out to Spectrum’s support for assistance with their product.