So, there are http response codes, you may know some of them like 404 means not found, and 500 means server error. Well 402 means "Payment Required" and has existed for pretty much as long as the internet. Just nobody used it, ever.
Coinbase, said "why don't we do something with that" and made x402 a standard to try to make it easy to accept crypto as payment. Eventually other people jumped on board, then it was finally handed off to the x402-foundation as an open standard.