git clone with https error - fatal: repository not found

I forked a private repository that I was invited to collaborate on but every time I try to clone with HTTPS, I get the following error message:

$ git clone https://github.com/usernamex/privat-repo.git
cloning into 'privat-repo'...
Username for 'https://github.com':usernamex
Password for 'https://usernamex@github.com':
remote: Repository not found.
fatal: repository 'https://github.com/usernamex/privat-repo.git/' not found

Note: 'usernamex' and 'privat-repo' are just examples

Here's some things I have tried with no success:

Verified the validity of the URL - Checked spelling and case. I am able to access the repo URL and download its contents through my browser by clicking the download ZIP button.
Asked owner to clone my fork - He had no problems cloning my fork but I do.
Contacted GitHub support...
Per GitHub support, cleared cached credentials - this is confirmed by the fact that the system requires my username and password with git clone and git push. In fact, I can clone and push other (public) repositories in my account.
Went through GitHub's HTTPS Cloning Errors guide with the exception of "Using SSH instead" because this doesn't really address the issue.
Viewed similar questions in stackoverflow.com - tried most suggested answers (see above).

I am running git 2.10 on a mac through Terminal and, as I mentioned, I am not interested in workarounds to HTTPS (e.g.: SSH or GitHub Desktop).

Any ideas why this is happening?

Solution

This Github document reads:

The https:// clone URLs are available on all repositories, public and private.

But since you are trying to access a private repository, authentication is required. One way is appending username and password the address as below:

git clone https://username:password@github.com/usernamex/privat-repo.git

But the same page reads:

If you have enabled two-factor authentication, or if you are accessing an organization that uses SAML single sign-on (SSO), you must authenticate with a personal access token instead of your username and password for GitHub.

If you have 2FA enabled, check this page for steps to generate a personal access token. Bear in mind that you should check full repo scope (as shown below) for your personal token.