I met some issue when I was trying to push my code to GitHub.

Pushing to [email protected]:519ebayproject/519ebayproject.git
To [email protected]:519ebayproject/519ebayproject.git
 ! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to '[email protected]:519ebayproject/519ebayproject.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Merge the remote changes (e.g. 'git pull')
hint: before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

I have not pushed anything in the repository yet, so why do I need to pull something?

This can cause the remote repository to lose commits; use it with care.

If you do not wish to merge the remote branch into your local branch (see differences with git diff), and want to do a force push, use the push command with -f

git push -f origin <branch>

where origin is the name of your remote repo.

Usually, the command refuses to update a remote ref that is not an ancestor of the local ref used to overwrite it. This flag disables the check. This can cause the remote repository to lose commits; use it with care.