Hi there and welcome
I want to make sure you did a full reset, as this nearly always clears the issue.
Please do the below
On Apple TV (4th generation), select Settings > System > Reset.
On Apple TV (2nd and 3rd Generation), select Settings > General > Reset.
Select Restore to return your Apple TV to its factory settings. Your Apple TV will also download and install any software updates. You need an Internet connection.
Let it complete and when it has, Showtime should then work.
Let me know how you go please.
Can you remove the power please to your wifi router, and the Apple TV and wait 5 minutes.
Then connect the power to the Wifi router and wait 5 minutes
Then connect the power to the Apple TV and tell me if it now comes up please.