when I copied a URL for cloning in Source Tree, it is stated under Repository Type that "This is not a valid source path/URL", but when I click "details", nothing is displayed in the pop-up. I am very certain that the URL I used is a valid one because it is a URL provided by our instructor at a coding class and everyone else managed to use it alright. (The URL I used was: https://github.com/code61/learning_html.git) I have tried reinstalling Source Tree and have also downloaded GitHub, but problem persists.

I have attached a screenshot of the problem.
It will be greatly appreciated if you could help me to solve this problem.