Am I the only one with trouble when trying to buy stuff right now, or is it a widespread issue?

Put in a ticket with GOG support and they will help resolve it. It may take a few days. Foreign or maybe just US transactions seem to get flagged by GOG's fraud prevention system. Also check with your bank to see the limits on overseas transactions before your credit card transaction is flagged for fraud by the bank and gets locked for GOG site.

A support team member was able to loosen the restrictions on mine and I was able to add to the wallet funds. Be aware that you may only be able to do one transaction. I tried a second one previously right after the first and got the "cannot verify" error.

As others said it's seemingly affecting a decent number of people....if it's fraud prevention then imo GOG should rework that bit of the code/site, as it makes people like me sometimes want to buy less(if I cannot buy at all due to such issues when using my preferred payment method).

Well, at least it isn't just me then!

I'd try another method like paypal/etc if you can and want to.....I tried paypal myself and it seems to work when the card I use won't work.

A bit, had a kobo sale going wrong ending up paying three times for an object....this matter still needs to be resolved,
and had it again when purchasing a new psu... leaving me with the same text: your purchase can not be confirmed, try to pay again <------ never belief this shit or look for other payment methods with this one being resolved immediatly..

Kobo seems to be a hoax platform regarding missed out payments or... checking their administration for purchases went wrong

I have paypal, but I don't think it will be enough. If I put my money to my paypal, it will takes few weeks to confirm the money that I put. And by the time it done, the summer sale will be over already.

As for other payment options, I am not familiar with it. It sounds like I will need to create a new payment account.

That is sad to hear....that said, one can link a card or bank account to paypal for unlimited access to said funds, if one wants and is ok with such.