Description: This solution discusses how to resolve this required field missing error using IOM default settings
If you are indicating anything regarding a "Participant" you will need to insert the "Event ID" column in your profile in order to have the participant information added appropriately. If you are using version 2.0 or above, you can insert the Event ID in a virtual column as well.
After you insert an Event ID in your data file and adjust your profile with the new information, you can attempt to import the data again.
Refer to the ImportOmatic User Guide for additional information.