To fix this, remove the deploy key from the repository, and add the key to your user account instead.
If the key you are using is intended to be a deploy key, check out our guide on deploy keys for more details.
This version of GitHub Enterprise was discontinued on 2021-06-09. No patch releases will be made, even for critical security issues. For better performance, improved security, and new features, upgrade to the latest version of GitHub Enterprise. For help with the upgrade, contact GitHub Enterprise support.
This error means the key you are pushing with is attached to another repository as a deploy key, and does not have access to the repository you are trying to push to.