Checkout branch on different remote

If you just added the remote, you'll need to fetch it so that Git knows which branches are available:

git fetch upstream master

After this you can do

git checkout upstream/master

without any issues.

In more concise way (I'm using git 2.28), you can say

git fetch upstream

and then

git checkout -b <branch_name> --guess

where the --guess flag checks if a branch corresponding to <branch_name> exists on any of the remotes and tracks the corresponding remote (docs here).

Just fetch the refs from the remote (this will fetch all branch, commit, refs etc for the upstream repo)

git fetch upstream

After this, checkout the needed branch (this creates a local copy of the branch)

git checkout -b <branchname> --track upstream/<branchname>

Now if you want to pull the changes in this branch in future, all you need to do is

git pull upstream <branchname>

---

As mentioned here, try doing an explicit fetch on the branch name:

git fetch upstream master:branch_name