They are screwing the pooch on the HBO Max roll out. Probably because they are trying to extract more money from the like of Roku and Amazon.
If you used HBO GO on older devices, you are likely out of luck. I have have 2015 Samsung TV that isn’t supported, also one at my mom’s house. The work around is to use my iPhone, HDMI adapter, and HDMI cable.
If you have a Firestick the workaround is to sideload the HBO app. I’ve done it on all 3 of my Firesticks and it plays HBO Max just fine. Whenever they come out with the official HBO Max app for Firestick I’ll have to delete the sideloads. Just google “firestick sideload hbo max”.