Getting "fatal: Authentication failed for..." error

[Amit.Karpol]

In SourceTree, I'm getting the "fatal: Authentication failed for..." error when I try to Push/Pull from origin. 

The Git terminal from SourceTree asks for my username/password and, when I enter it, it works correctly (I'm able to do a push/pull anyway). However, nothing I've tried will allow me to use the push/pull buttons in SourceTree. I've updated my Git username every place I've been able to see something that resembles a username, I've gone to Tools > Options > Authentication > [My Account] and set the password (which is a private access token).

Details:

- SourceTree version 3.3.8.3848

- Windows 10 Pro, 64 bit

- origin server is Visual Studio Team Services

I'm not sure why it stopped working (I haven't changed my VSTS password and all my private access tokens are still valid), but I seem to recall an odd password box that popped up a week or so ago that I believe came from SourceTree. I might have entered the wrong password, but didn't see any problems at that time (I haven't pushed/pulled since then, so wouldn't have seen any problems until today).

saw an answer that was given by David Keck:

"The only thing that worked for me was navigating to C:\Users\USERNAME\AppData\Local\Atlassian\SourceTree and removing the passwd file."

but I can't see the file "AppData" on my computer. 

What am I missing?