Short answer: This error means the branch you want to push in remote doesn't exist!
In my case, starting from October-2020, the repos created since then had the main branch instead of the previous master branch. So all I had to do this:
git push -u origin main - you may skip -u flag if the upstream is set( Like in case you had cloned it already)
Bingo! That worked for me! Hope that helps! Happy coding!