This worked for me when I got error code 3. I did not use my email, but just the username. Instead of firstname.lastname@example.org, I just typed in username. Hopefully this works for others. (Note, this was for the app, not spotify.com)
@d1rtgrub wrote: So I figured out how to fix mine, but I'm not sure if it will work for others. Basically what I did was go to my email that my account was registered under and I searched for an old reset password email (thankfully I had one from like 2 days before) and I just reset my password with the link and now it works fine! I hope this helps!