I currently have a Contractor on site to obtain information through Survey123 App. But he recently reported that he is unable to upload / submit completed questionnaires. I tried on my phone (iPhone 7) and it works fine. He has been copying completed Questionnaire's data and updated it as required before submitting, if that may help to understand circumstances that could lead to issues. The Contractor has an iPhone 7.
Any suggestions on probable causes, and troubleshooting I can advise would be great.