336 FTP Reply Code - KB Article #1543Related Articles --
336 Username okay, need password. Challenge is...
A 336 reply code may be sent in response to a USER command where a challenge is to be presented to the user in order for them to provide a valid password. The client should immediately respond with a PASS command. This response is intended to be presented to a human user and so the format of the challenge should be understood by the user.