It's a payment problem but in this case I've already paid a game... but no game after payment collection.
I had a similar issue at the end of September (tl,dr: support solved the issue in three days). I googled for a solution, ultimately decided to contact support for the first time, but I contacted support, I think, 7 days after the purchase (I wasn't in a rush, thought to see if the issue will go away by itself).
I hope this helps you in some way.
Funds were deducted from my card and I received an email receipt, as usual, but no games and the order was not showing in the Orders History page on GOG site. And previous purchases from that day went through with no issue.
I wrote a ticket (again, 7 days after the purchase), I elaborated as much as I could, included dates and so on. I even attached a screenshot of receipt I received in my mail.
Got an automatic answer first, with "I got charged and did not get my game"
as a suggested solution, to which I replied no, because I knew funds from my card went through, according to my bank, and the purchase included full games, not DLCs.
The next day I received an email "We’d like to let you know that your ticket (#Ticketnumberwashere) is currently being processed, and one of us will get back to you as soon as possible."
And day after that a support agent contacted me with an email and, that was it, games were in the library.
It's the same scenario but I have yet to have any form of human answer from anyone from GOG and it's been 5 days already.