Unable to do git clone using ssh keys

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Hello,

We are unable to clone a git repo using SSH keys after configuring ssh public key on the profile level.
GitLab version 12.4

getting the below error when trying to test ssh:
$ ssh -T git@demouser@serverIP

**git@demouser@serverIP: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).**

Could anyone please help with this ?