I have HBO Max on my phone which is LG and Chromecast which is hooked up to the TV in one room. In another I have a Roku 3. I received HBOMAX through a promotion from At&t. I have the app on Roku installed but I can't watch anything because Roku 3 wants me to subscribe with a pin number. Can you help?
I would expect you should contact ATT or HBO Max
https://help.hbomax.com/ContactUs
I expect ATT didn't exactly give you HBO MAX. They gave you ATT MAX on ATT.