Verify that you downloaded/installed the correct Showtime Channel/app. There are 3 available. One is Showtime (direct subscription streaming), another is Showtime Anytime (cable provider required), and the third is Showtime on the Roku Channel. (purchased through Roku and accessed through Roku Channel)
If you subscribe to Showtime directly, then download Showtime. (Red box w/ white letters). This is the one that you need to use to enter your login credentials and stream your Showtime content through.
You can find them using the Search or Streaming Channels feature from the Home Screen.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102
Great information. Thanks. But I cannot watch on my phone or tablet with 'Showtime on the Roku Channel. (purchased through Roku and accessed through Roku Channel)'. I went through Roku. Showtime is the most difficult to access - because they have too many choices(?). All other similar platforms whether I have a subscription or am on a trial I can them access on my TV, phone or tablet. Showtime is annoying and it makes me not want to end up subscribing. They need to catch up technologically speaking. If I'm a passenger on a road trip and I wanna watch "Your Honor" on my phone or tablet, why can't I do that? So annoying.