It's not going on discounted games.
What is going on?

No offense but you've given us zero details to go on.

We just talked about the issue here:

https://www.gog.com/forum/general/cant_pay_with_card

If that doesn't help, some details as to your setup and what you;re trying to buy would be helpful as a start.

My guess from previous threads is that you;re trying to buy a DLC for a game that's not in your library or you're trying to gift a game when you;re not allowed to. Again without knowing what you;re trying to do, it's kind of hard rto point you in the right direction but that thread lists a few of the problems.

Hope this helps

It;s not working buying discounted games. Tried many.
Is working option "Buy for somebody".
All others not working.

My Windows is 7.

Which games have you tried to buy?

YES IT WAS DLC. Sorry and thanks.

Not a problem. If you don;t have the game purchased, it won;t let you buy the DLCs.

Glad you figured it out.