Cannot purchase in TV app on Mac

Sometimes I am not able to make purchases in the TV app on Mac. When I try, the fingerprint icon does not appear in the purchase dialog. (See image.) Pressing the TouchID key does nothing. There is no option to enter a password. My only available option is to cancel.

This applies both to shows also available through a connected streaming service and to other shows. In the first case, even if I am able to stream a show for free, I might want to purchase it for reliable viewing at a later date. In the latter case, I don't know why I wouldn't be able to purchase.

I've double-checked my payment method, and don't see any problem there. I am able to make the same purchases on the same account in the TV app on my iPad.

[Edited by Moderator]