Can't SSH Key

[Lakshit Singh Bisht]

"error - key: Someone has already added that SSH key."

I am getting this error while adding my ssh key for signing commits. 

1. Technically I can use same key for multiple purpose, so why is bitbucket showing it?

2. I have added same key in Github, Gitlab, Codeberg, and Gitea. There no problem and commits are signed automatically