On a Mac, whenever I try to clone a repo, I get "Authentication Failed", please help!

I am just the composer and sound designer for a game. I am brand new to GitLab and am being walked through this process by the head game developer, but we’ve run into a wall.

Whenever I try to “clone a repository”, I type in the correct address, it tries to connect to it for a second, and then it says “We were unable to authenticate with gitlab.com. Please enter your username and password to try again”.

The username and pw is 100% correct. He said something about installing the Command Line Tool, which I did, but from this point I am completely lost as I don’t have the slightly inkling of coding knowledge. And I am doing all of this on a Mac.

Any help would be so much appreciated!!! Thank you!!