Why is it giving the error 'failed to push some refs'?

Question

GitHub

When you enter this command: git subtree push --prefix dist origin gh-pages
Error occurs:
git push using: origin gh-pages
git: 'credential-manager-core' is not a git command. See 'git --help'.
git: 'credential-winstore' is not a git command. See 'git --help'.
git: 'credential-manager-core' is not a git command. See 'git --help'.
git: 'credential-winstore' is not a git command. See 'git --help'.
To https://github.com/invex0811/salary.git
! [rejected] ae55975dba5f8655c344328e5175d4d34b04e7bd -> gh-pages (non-fast-forward)
error: failed to push some refs to ' https://github.com/invex0811/salary.git '
hint: Updates were rejected because a pushed branch tip is behind its remote
hint: counterpart. Check out this branch and integrate the remote changes
hint: (eg 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

Already tried to clone and shoot, nothing helps (