How do I log into Sundance App on my Apple TV using my xfinity login?

Please try using your TV provider credentials for sign-in, if the TV provider plan should give you access this service, and if Sundance supports this type of sign-in in their app.

I don’t see these listed, though.

Apps that let you sign in with your TV provider on your iPhone, iPad, or Apple TV - Apple Support

Use your pay TV or cable provider with Apple TV - Apple Support

TV providers that let you sign in on your iPhone, iPad, or Apple TV - Apple Support

Else you may need to use the Xfinity Stream app (requires tvOS 15.0 or later) on the Apple TV box to access this channel, instead of the separate Sundance app.

Sign into the app using your xfinity account and password.

Xfinity does not let you sign into other subscription services from Apple TV. They want you to use their service to access other subscriptions. If your TV supports downloading apps, you can use your TV to access Apple TV and use your Sundance subscription within the Apple TV app.

That is different from my Xfinity Service. I have a Max and Apple TV subscription, but cannot access Max in the Apple TV app and have to use the Max app on Xfinity. When I use the Apple TV app on my TV, I can access my Max subscription through the Apple TV app. Keep us posted on if you find a solution as I think that would be beneficial as well.