When you are done, make sure a working demo of your project is hosted somewhere public.
When you submit the URL to the GitHub repository, it won’t work because the repository is having the source code. The test requires a running server. If you are hosting the project on repl.it, then make sure the project is running and you are submitting the correct URL.
I suggest you clone the FCC repl.it starter project and proceed from there. I hope that helps.