Probably as mentioned by others this will be a case mismatch in branch naming.

If you have such situation I can guess that you're on Windows which will also lead you to:

$ git branch -m CaseSensitive casesensitive
fatal: A branch named 'casesensitive' already exists.

Then you have to due an intermediate step:

$ git branch -m temporary
$ git branch -m casesensitive

Nothing more. Hope it helps! cheers

Probably as mentioned by others, this will be a case mismatch in branch naming.

If you have such a situation, I can guess that you're on Windows which will also lead you to:

$ git branch -m CaseSensitive casesensitive
fatal: A branch named 'casesensitive' already exists.

Then you have to do an intermediate step:

$ git branch -m temporary
$ git branch -m casesensitive

Nothing more.