Error in Visual Studio on GIT PUSH: Failed to push to the remote repository. See the output window for more details.

In Visual Studio, when trying to push code, this is a common and mildly annoying message because it isn't clear about the problem.

Ok, lets look in the Output window. This is not helpful, it is not showing anything. To be fair, it usually defaults to something but never the correct output window. I have not seen it blank before!

Make sure you choose the correct Output Log, which in this case is "SourceControl - Git"

Ok, we can now see that Authentication has failed. I'm not sure why it doesn't just popup and ask for credentials. That would be helpful.

Anyway, it is easy to fix.

Back in the Git windcow, click on the Sync Icon (two curved arrows arranged in a circle).

That will trigger a sync, which will popup the credentials window. Once authenticated the sync will proceed and it will Pull then Push.