Cloud Gaming Does Not Work

I recently purchased the Ultimate Pass Subscription. I tried to run a game today on my MacBook through the Safari browser but on almost every game the "PLAY" button is greyed out except Fortnite. But when I click play on Fortnite there comes an error message.



I hope someone can help me

Edit: It might be important; I ran a game through GeForce Now and it worked there.

:)