Permission Denied problem when using git deployment

Followed https://www.digitalocean.com/community/tutorials/how-to-set-up-automatic-deployment-with-git-with-a-vps

When trying to push live master

i get the following error in my local machine

Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

I have setup ssh keys

i mean created public key, private key and added public key to /.ssh/authorized_keys of server

but still its not happening…

I guess I have made ssh via password login disabled, is that causing teh issue

ssh ubuntu@128.199.165.57 will not work

but however the following command ssh -i ~/.ssh/id_rsa_xyz ubuntu@myhostname works

pls clarify what am i missing

or what should i do to make git use ssh key for authentication when working with digital ocean