Yeah I know you are referring to the fiat-based financial system. Keep in mind, wire transfers generally cannot be reversed. There have been notable instances where money is lost/stolen this way, and no way to get it back.
Yes, they can.
If it's a significantly large sum, it may look like this:
Step 1: The CEO of the debtor bank calls the CEO of the creditor bank and asks to return the money.
Step 2 (only needed if there is disagreement): Lawyers of the debtor bank send a ton of legal papers to the creditor bank and figure it out.
But it's just one of nearly infinite number of scenarios.
6 billion in fiat is too large a figure to be irreversible. Do you have any examples?
And yet somehow nobody hears about North Korean hackers stealing billions from regular banks.
Wire payments are definitely reversible, but you might need to involve the courts, and international wires are more complex [0]. Most notably, 900 million in accidental payments made by Citi were eventually fully reversed by appeals courts.
> A full recounting of it is outside the scope of this anecdote, but it rhymes with “If you and the United States federal government disagree whether a transaction is final, you are wrong.”
[0]: https://www.bitsaboutmoney.com/archive/no-payments-are-final...