Fatal: Not possible to fast-forward, aborting

Why this problem?

This happens is your branch is no longer directly based off of the branch you’re trying to merge it into - e.g. another commit was added to the destination branch that isn’t in your branch. Thus, you can’t fast-forward into it (because fast-forward requires your branch to completely contain the destination branch).

Solution that works for me is from StackOverflow

git pull --rebase