Git merge develop into feature branch outputs "Already up-to-date" while it's not

I checked out a feature branch from develop called branch-x. After a while other people pushed changes to the develop branch.

I want to merge those changes into my branch-x. However if I do

git merge develop 

it says "Already up-to-date" and doesn't allow me to merge.

git diff develop shows that there are differences between branch-x and develop.

How do I merge develop into branch-x?

You should first pull the changes from the develop branch and only then merge them to your branch:

git checkout develop 
git pull 
git checkout branch-x
git rebase develop

Or, when on branch-x:

git fetch && git rebase origin/develop

I have an alias that saves me a lot of time. Add to your ~/.gitconfig:

[alias]
    fr = "!f() { git fetch && git rebase origin/"$1"; }; f"

Now, all that you have to do is:

git fr develop

Step by step self explaining commands for update of feature branch with the latest code from origin "develop" branch:

git checkout develop
git pull -p
git checkout feature_branch
git merge develop
git push origin feature_branch

git pull origin develop

Since pulling a branch into another directly merges them together

git fetch && git merge origin/develop