I use PayPal for pretty much everything online. Today, I get this message on the payment screen:

"Selected payment method is currently unavailable, please choose a different one."

Anyone else getting this?

Have you tried restarting the PC?

First, go to paypal's website, then log into your account. Next, then go back to GOG and pay for your items with paypal by logging in to Paypal from GOG.

Paypal, for some strange reason, forces you to do this in order to pay for items on GOG.

^ +1

Or if the OP uses either of those, he/she could at least find the paypal-related domains and create exceptions for them in the extension.

I do, have you expanded the payment option box and tried to reselect paypal?

Thats what I have to do

Best in some cases to hit the red ! to give the tab all permission during payment... Nothing like having to reload the same page several times because needing certain scripts...