I am brand new to freeCodeCamp. It seems that CodeCamp expects a url to CodePen.io for solutions.
I am not sure how that works. Codepen only has html/css/javascript sections. There is no option to host a file.
Which project is that for?
My suspicion is that the placeholder text you are seeing is used in all project submission pages, and is more relevant to the frontend projects.
That said, the placeholder only uses codepen as an example - you can use any hosted version, such as Glitch or a Github repo.