GoG has always been a problem, with fraud prevention, for me. But, recently, it's gotten really bad, to the point that I've skipped purchases, for not wanting to wait around in a bank branch office. By the time I could get money into a wallet, or on my Paypal account itself, or other similar methods, sales I want to take advantage of may well be over. They're not the only ones, or by far, these days, but others that trip credit or debit fraud triggers (such fraud prevention has never caught any actual fraud, though), will automatically retry the transaction. So, I'll get an email or phone call, go through the process of saying it's OK, it gets retried at some point soon after, and all is good...except here.

Is there any way to get them to do what most others will, and retry the failed transactions, after authorizing them? Alternatively, can they do a raincheck?

Why not put the money there before a sale?
It won't vanish.

Anywhere it would be safe, it wouldn't be in a place for international transactions. As to adding it to some wallet, how much, and when? Or, what about things just working? Paying for software from Europe is not an uncommon thing, nor are fraud alerts from that, and GoG is the only one that, "stays failed," after authorization.

https://www.gog.com/en/wallet
Of course it would be (both: safe and in place for international transactions). How much do you intend to spend?
That's a question, nobody but you can answer.

When?
Whenever you feel like it.

But probably best before a sale comes around - since you (allegedly) can't put money in your wallet, as soon as that happens.
shrug

Gog has a Wallet for this very problem. The company has a habit of not budging on everything it does wrong, that self harms. So if the customer cant change. The company sure wont.

What about PaysafeCard? Can be bought in stores with cash (or credit card if need be), is designed to be private and secure so there can't be fraud concerns, can be bought in the US of A and GOG accepts it as payment method, so probably doesn't even need currency conversion. They usually hang next to the cashiers along with the Steam and other prepaid vouchers, though their bland appearance doesn't make them stand out so noone ever takes note unless they already know what to look for. Well, I guess now you do. :)

I prefer this to wallet funds, because 1) a wallet is tied to the account and if the account is compromised, so is the wallet, and 2) can't be reattribauted once it's in the wallet, so if I wish to buy somethinge else, I can with PSC but can't with wallet funds.

Of course, you absolutely must keep the code safe, because that's all you have as proof. The voucher printouts will fade, so rewrite it with something durable like a biro if you wish to stack them for later use. And if anyone else can read or photograph your voucher then they can redeem it in your stead.

Paysafe is not sold in america like a gift card. That is only in europe, in some locations.

OK, I assumed it was the same over there, since Wikipedia listed USA just like any other, but they say "paysafecard is distributed countrywide by various external partners, which is why the types of shops offering paysafecard vary by country.", and given the size, in the USA that might even vary between member states, but still there should be some way of obtaining these things over there?