Merge and Data mapping failure

I am using a contact to send a document for signature. The contact is a student. The recipient of the document for signature is *not* the student, but the email address of the student's parent which is a field within the Student contact.

The Student's name does get correctly added to the title of the email using the {!Contact_Name__c} 

so I know the correct contact is being accessed.

I am trying to merge the student's name into the document before sending using merge mapping but I get the following error:

Object look up field: echosign_dev1__Recipient__r not set, ignoring mapping entry

I am also trying to store the signed document in the contact's Notes and Attachments section but this also generates an error:

Attempted to map to a related object reference which was not set on the agreement: echosign_dev1__Recipient__r.

I suspect that the error is because the recipient of the document (the parent) isn't the contact (the student), but is just a field within the contact, but I'm just guessing. I have opened a ticket with Adobe but am hoping someone else may have some ideas. I am using Adobe Sign version 18.27