I created a relatively simple Excel survey on my OneDrive and then asked about 50 people to complete it at once. About half successfully completed it but at least 2 people on iPhones had a problem ("Problem Submitting Survey". Contact the person who sent you this survey."). One suggestion I have seen is to not make the fields "required" but I want everyone to complete all the fields.

Any ideas please?

Hi,

Did the 2 people open the Excel survey with Safari? If yes, there might be some issues between  Excel survey and Safari. Please try to use other browser to test, for example, Chrome.

Please see this similar thread:

https://community.office365.com/en-us/f/172/t/360665

Regards,