Why does fetch from an existing remote repository report that the repository does not exist?

[mheins57]

I have SourceTree 4.2.0 on a Mac Mini running Monterey 12.6. I have admin access to an existing repository owned by someone else.  I can successfully perform a command line "git fetch origin" in my local cloned copy.  If I open the local repository with SourceTree I can see all the branches and files properly.  However, when I attempt to do a fetch, I get the following error:

git -c color.branch=false -c color.diff=false -c color.status=false -c diff.mnemonicprefix=false -c core.quotepath=false -c credential.helper=sourcetree fetch origin
remote: Repository not found.
fatal: repository 'https://github.com/beezwax/InspectorPro/' not found
Completed with errors, see above

If I do a "git remote get-url origin" with the command line, it shows:

https://github.com/beezwax/InspectorPro

so the path SourceTree is using is apparently correct.  What is wrong, and how do I fix it?