Fortnite account cousin?

My cousin has logged on to a website and tries to buy an acc but then came an error and he had npch his money he can be banned for it and if he bought the account anyway

Yes, Epic Games is relatively quick and happy to ban accounts that are to be sold or bought. Something like that is also illegal and Epic is there afterwards and banishes the accounts permanently, so getting money back is not to be expected. So it's a good thing that you're getting an error.

Good that he couldn't buy it

But what does error mean?

Most of the time, error only means that something went wrong. Perhaps the site would have a very short wave where nothing can go and you probably got it, don't know how to explain it… Something went wrong with Error.

Okay did the research again, that means error exactly:

An error message, English error message, is a reaction of a computer program to a detected program error or a known error situation