Existence of 402 doesn’t really say much. 418 and 451 are probably just as popular error codes as 402, but nobody would argue any of these codes are a material

Existence of 402 doesn’t really say much. 418 and 451 are probably just as popular error codes as 402, but nobody would argue any of these codes are a material part of the HTTP core. Moreover, there’s no special functional purpose to 402, not in the RFC and not real life.