A required element must have at least one file uploaded by the user before the form can be submitted.

Making an element required

File Upload → Settings

Tick the box at the Required field to make it required.

Required error message

File Upload → Settings → Optional

Change the required error message by entering text into the fields under Translate error messages.

Required indicator text

Settings → Style → Labels

Change the text indicating the element is required. By default this is (required), but you may want to make it an asterisk * for example.

Still having trouble? Head over to the forums.