Are you referring to the Spectrum TV app? If so, it is not supported on Fire Stick or Fire TV devices.
You do, however, have access to each networks' individual apps that you would sign in using your Spectrum login and password.
Currently the Spectrum TV app is supported on Roku, Apple TV, Xbox One, many Samsung smart tvs, iOS and Android mobile devices, and Kindle devices.
Each application is different, depending on the network.
You can find a list of networks and what devices they are supported on
You do have to subscribe to the channel to be eligible to use them.
Spectrum-Social Media Customer Care
Lead Moderator-Community Forums