I can't watch Apple TV+

I'm on a Mac, visiting the Apple TV+ web page. It keeps asking me to start a free trial. I've been subscribed to Apple TV+ for months. If I try to start a trial, it tells me I'm already subscribed but it doesn't let me play videos. The app is only available for iPhones & iPads.

My browser is up to date, my billing is up to date, I can't think of anything else prohibiting me from watching shows.