git@github.com: Permission denied (publickey).

This error message usually occurs when attempting to push or pull from a Git repository on GitHub without proper authentication.

To resolve this issue, you can follow these steps:

1. Make sure you have set up a SSH key on your computer and added it to your GitHub account. You can follow the instructions on GitHub's help page for Generating a new SSH key and adding it to the ssh-agent and adding it to your GitHub account.

2. Check that you are using the correct SSH URL for the repository. You can find the correct SSH URL by going to your repository on GitHub and clicking on the green "Clone or download" button. Make sure you are using the SSH URL, which will look like `git@github.com:username/repository.git`.

3. If you have already set up your SSH key and are using the correct SSH URL, try running `ssh -T git@github.com` in your terminal to check if you are properly authenticated with GitHub. If you receive a message like "Hi username! You've successfully authenticated, but GitHub does not provide shell access.", then you are authenticated and the issue may be with your repository permissions.

4. If none of the above steps work, you can try removing and re-adding your SSH key, or contacting GitHub support for further assistance.