Hey, I just wanted to share this.
When pushing to GitHub from Sourcetree, git prompted a pop-up window called Credential Manager, and to my understanding that window helps authenticate you as a user- to check if you are allowed access to the remote repository. I started by clicking “no-helper” as this window did not pop up in the tutorial, and doing that seemed to cause an unsuccessful push. The issue was resolved when I instead picked “manager–core” in the Credential Manager window.
I know this doesn’t provide any deeper understanding of what’s going on, but I thought it might help others push this issue aside (excuse the pun).
Have a great day 