Pushing changes to Git repository results in 'Updates were rejected' error, how to fix it?

I have an online repository on which I am the only person that can push commits, and there are no more branches than the main one. I have been working on it these days, and pushed commits without an issue, including folders and files etc.

Except today, when I try to push changes to update the repository with the latest files and folders I have, it gives me this error:

error: failed to push some refs to 'https://github.com/repo.git'
hint: Updates were rejected because the tip of your current branch is behind
To https://github.com/repo.git
hint: its remote counterpart. Integrate the remote changes (e.g.
!	refs/heads/main:refs/heads/main	[rejected] (non-fast-forward)
hint: 'git pull ...') before pushing again.
Done
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

I am using Pycharm Community Edition 13.2, and always update by selecting the Commit section in the left bar menu and then writing a comment and pushing the commit like in here:

I also never touched the online repository to make any changes, always kept local files which were then pushed. I already tried to fetch and to update the project but it didn't fix, so before I break my repository I want to ask for help

EDIT: I did make some changes to the online repository. I had added a LICENSE.md file which shows up in my remote history changes.

You say that you are the only one who push on that repository, but Github tells you that your head is older (behind) the remote one.

Before of all, I suggest you to inspect the remote history to check if somebody (?) pushed something else.

If you will discover some remote changes you should do a git pull with a rebase by git pull -r.