Spectrum works on my iPad but not on apple tv

The Spectrum TV app is available for Apple TV (4th generation or later), tvOS 13 or later.

Identify your Apple TV model - Apple Support

If you are trying to airplay then be aware that it is up to the provider to support it. If it is advertised to work then you would need to consult with the developer. Apple TV also supports native apps so you can go to its App Store to download from there to play direct from that interface.