The message you “need to complete the task first” means that when you completed the project, it didn’t get saved to your freeCodeCamp account (“Step 1” on the project page). Something maybe just went wrong with the request. You should be able to complete that by following the steps here. I think they’ve worked for pretty much everyone with a similar issue.
After you get the checkmark by that “Step 1”, you should be able to submit your URL.