Adobe Sign - Webform Error

[asu-jjdavis1]

I am trying to create my first web form that would include the main signer (participant) and then an optional 2nd signer (participant). For the instructions of the 2nd signer, I made a note that it is for Parent (if under 18) to match up with our current form and I unselected the required checkbox. However, when I click next to move to the assigning the fields, I get an error statying "Adding unknown partipants for webforms is not allowed". I have looked through all of the settings and can't seem to figure out why this is happening. If I don't add the 2nd signer, the form progresses without an issue.

Any ideas on what I am overlooking in the group settings?