A similar issue is described here however, my symptoms are a little different and none of the steps there seemed to work. Nor does the suggestion here work.
I'm attempting to use SourceTree to clone a private repo belonging to github organization of which I am a part. I have full permissions to view and commit to the repo, I can see it online when I log in, AND I can clone just fine with the command line and also via the github desktop application. It only fails in SourceTree.
Further, it is not bad credentials or anything like that, because I can clone, commit and push to my other non-private repos on github using SourceTree with my github credentials.
From the "Clone a Repository" dialog I enter the source URL, which looks something like this:
https://github.com/MyOrgName/reponame.git
I tab off of that field and it populates the destination path and name fields, but at the bottom of the dialog is a yellow exclamation point with this error:
This is not a valid source path / URL
If I click the error message, it brings up the "Details" dialog, which states the following (twice for some reason):
remote: Repository not found.
fatal: repository 'https://github.com/MyOrgName/reponame.git/' not found
remote: Repository not found.
fatal: repository 'https://github.com/MyOrgName/reponame.git/' not found
I have also tried this by adding my username to the url like so:
https://myusername@github.com/MyOrgName/reponame.git
but no luck there either.
It happens because Sourcetree didn't get some private access from Github while authenticating. So the solution is very simple.
Login to your Github account on any browser.
From the top right corner select SETTINGS.
Now select DEVELOPER SETTINGS.
From DEVELOPER SETTINGS select PERSONAL ACCESS TOKEN.
Now from PERSONAL ACCESS TOKEN select GENERATE TOKEN.
Fill Note as Sourcetree
and Check All Scopes from the checkbox as shown in the below screenshots.
Now Open Sourcetree.
Click on Options in Tools menu & Click add Account.
Enter username as your Github account username and password as Generated Token from Github.
Click on SAVE now you might see all your repository are visible and can clone too.
Hope it helps.