Having trouble downloading Git archive tarballs from Private Repo

I need the ability to download our application at specific tags, but I am unable to find a working solution for this. Downloading tarballs based on git tag seems promising but I am unable to get it working using Curl. I have tried the following but all I get back is the source for the github 404 page.

curl -sL https://github.com/$ACCOUNT/$PRIVATE_REPO/tarball/0.2.0.257m?login=$MY_USER_NAME&token=$MY_TOKEN > 0.2.0.257m.tar