HTTP 402
HTTP 402 Payment Required is a web status code set aside for payments. It has no agreed use, and some schemes for paid AI crawling are trying it out.
HTTP 402, Payment Required, is a status code a web server can send back instead of a page, telling the visitor they have to pay to see the page. It was set aside in the early days of the web for digital payments, and then mostly left unused.
It's come up again because of AI. Some publishers and infrastructure companies want AI bots to pay to read their pages, and a status code that literally means "payment required" is an obvious place to start.
Where it stands
The MDN page on 402 calls it a nonstandard code reserved for future use. There's no standard way to use it, and different systems use it in different ways. Browsers don't do anything special with it either, so a person who hits one just sees an error.
Some schemes for paid crawling are experimenting with it: a bot asks for a page, gets a 402 with a price, and can pay and try again. None of them is a standard yet.
What it means for you
For example, say Fernhill Coffee's host offers to charge AI bots for each page they read, and Fernhill turns it on. The bots that pay keep reading. The ones that don't get a 402 and move on, and the platforms behind them may stop using Fernhill's pages in their answers.
That's a fair trade for a publisher whose pages are the product. For a brand that wants to be recommended, it's usually better to let the bots in.