After the applicant has filled out their full application, and are on the final submission screen, a popup may appear that reminds applicants to double check each section of the application and make sure they are all complete.
A blue message at the top will identify any issue with the application, for instance if required documents are not attached to the application. If a document issue, go to the documents section and click Edit next to the documents header to ensure that all of the uploaded documents are actually tied to the required document request.