https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/402 HTTP Status Code "402 Payment Required" → This status code is reserved but not defined.

Actual implementations vary in the format and contents of the response. The original intention was that this status code might be used as part of some form of digital cash or micropayment scheme .. so if you have interest in eCash, Bitcoin or any other form of digital money protocols for the future - join in, discuss, experiment.