I've put up new draft docs for the next Pinboard API version—take a look! The first is an overview: https://pinboard.in/api/v2/overview The second is an API call reference: https://pinboard.in/api/v2/reference/ … I'm sure I've missed stuff, so ping me here or at the Google group: https://groups.google.com/g/pinboard-dev/c/a5aQscw4uVE …
As I understand it you should get a 403 for the valid username + wrong password combo