I can not download apple tv app onto my ipad i already pay for it on my my iphone

The Apple TV app with its current services such as Apple TV+ and Apple TV app Channels requires the latest version iOS/iPadOS. Some older models iPad may not be able to upgrade to the latest version.

Which generation is that iPad Mini?

The TV app is preinstalled with IOS, make sure your iPad is up to date.

It is far from being up-to-date, please update it.

The original TV app was released with IOS 10. You would need IOS 12.3 or later in order to have the redesigned TV app, with Apple TV +

You probably have the 1st gen then, you would need at least a 4th gen, which was released in 2015.