Permission denied problem when key exists

I am not able to push a forge site to my git repo with the error:

[email protected]: Permission denied (publickey). fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists.

This error clearly indicates that there is a permissions issue, however I have confirmed the key is set up in github and I am also able to push other sites from my forge account without any problems.

Can anyone shine any light on this issue and how I might fix it?