this is probably a silly question, but I could not find any answer here or on the Nuki Website. And I don’t own a nuki (yet):
Is the usage of the Web API for free? And is it limited to a number of requests per day or month? I could not find any pricing information.
Free and not limited (but there are some SPAM/abuse protection measures in place).
If the API is free, why is there a response code 402 (“Account not payed”) on this endpoint?
This was an option for “Box packages”, to have the separate possibility to charge für sub-users of a Nuki Box, by restricting the time and number of free authorizations for only those account types.
This has nothing to do with the API access and is not even in use anymore as with the new Box offer everything ist included in purchase like for a Smart Lock/Opener (see Nuki Box - turns entry intercoms into smart door locks).