My company just enabled SSO for my Github Org overnight so was getting the same error running git pull. I fixed this with the following steps.
- Open Credential Manager in Windows and delete the existing credential for github.com
- Re-initialise the cred manager in git bash:
git config --global credential.helper manager-core - Re-run
git pulland follow the pop-up instructions to authenticate in a browser (which happened automatically for me with SSO).
After those steps git commands worked for me again.