GitLab: Merge blocked: fast-forward merge is not possible. To merge this request, first rebase locally.

If you are working with Merge Requests in GitLab, you may see this message quite often. So what can be done to fix this and merge the branch?

So what is wrong?

If you go to any merge request displaying this message, you will see that the branch does not have all changes from the main branch. Also, GitLab cannot rebase this as…