A submission is marked incomplete for a number of reasons. The most common are:
- Missing, wrong, or unmarked README
- Missing or invalid GIF
- Inaccessible repository
- Incomplete required stories (for remote courses)
A comment will be posted in your repository with more details on what exactly is lacking in your submission. If you are not getting notifications from your GitHub account, make sure you are not filtering out email notifications from GitHub and have your GitHub notifications setup properly.