This question is in reference to Atlassian Documentation: Someone has already registered that SSH key
I'm getting this error message after trying to register my public key in one account, but I had the same public key also registered for another account.
So a person cannot have the same public key loaded into two different accounts? Why?
Correct. It's due to ssh (which git is using as the transfer protocol) uses it to identify you as well as to verify you. See https://www.quora.com/Why-cant-I-add-my-public-SSH-key-to-more-than-one-account-on-GitHub