PSN has a stupid problem.
There are three ways to buy a game (now 4).
PS Plus
PS Store normally
PS Now
If you have a game on PS Plus and want to buy it on PS Store normally, you have the message don't support and ask them to remove the game from your PS Plus so you can buy it. You might want to do this if a game was 50p in a sale and you wanted to let your PS Plus lapse.
Annoying but not a big deal.
But also, if you own a game on PS Plus and then play it on PS Now, it automatically removes it from you PS Plus!