Why do I canstantly have to re-authorize my imac to watch apple tv, and it STILL wont let me watch my purchased movies and shows

Today when I tried watching a purchased show on my iMac, the Apple TV app wouldn't let me. The "authorize computer" pop up kept popping up instead, and no matter how many times I authorized this computer (which was already authorized to begin with) or restarted the computer or the app, it wouldn't let me watch and instead kept forcing me to authorize the computer, over and over and over. I bought these movies and shows. Why am I having to deal with this? It is SO FRUSTRATING.