MacRumors:

HBO today announced that its HBO GO and HBO NOW streaming services will no longer be available on second-generation and third-generation Apple TV models starting April 30, 2020.

HBO says this change is being made “in order to provide the best streaming experience.”

I hate that kind of weaselly PR speak. If you are affected by this, there are some options still available to you such as using AirPlay or an HDMI cable to connect.