Official comment
Try logging out of your Beatport account from within rekordbox, reboot your computer, then login again. If you still encounter and error, please file an inquiry ticket here and attach a copy of the Beatport log, found at:
Windows - C:\Users\username\AppData\Roaming\Pioneer\rekordbox\Beatport.log
macOS - /Users/username/Library/Logs/Pioneer/rekordbox/Beatport.log
...and our support team will gather some additional information to assist you in resolving this issue.