Created a new Last.fm account. When I got to login in profile settings, it fails to login. I’ve checked very carefully that I’m using the correct username and password.
Can you confirm that you’ve “verified” your account and everything from Last.fm (typically an email is sent to you at signup to do this).
If you have, can you confirm that you’re able to log in with the same credentials from the an incognito browser on the Windows PC you’re using as your Core?