Official comment
David,
Are you planning on using rekordbox 5 or 6? If it's 6, you don't need a license, just connect the DDJ and play. If it's 5, you would only be able to use the same account you previously had the license key activated, and on a maximum of 2 computers. If you have exceeded that number of installs, or the computer name has changed, then we can reset it for you - please file an inquiry ticket here and our support team will gather some additional information to assist you in resolving this issue.