Dynamics 365 CE requiring a contact mobile phone number??

Hello,

We are using Documents Core Pack in Dynamics 365 CE to merge several Adobe Sign template documents.  The templates are assigned to a Custom entity, but also reference a related contact record.  None of the templates reference the contact phone number, however, I get the error below if I attempt to send to a contact that does not have a mobile phone number set.

It seems there must be a setting somewhere to require a mobile phone number, but I don't see it either in the Adobe Admin Console, or D365 Adobe Sign Settings.

Error while generating eSignature: Error during update 'adobe_agreement' entity in CRM (agreement has not been sent): The given key was not present in the dictionary.|
at AutoMergeService.MergeService.SignDocument(IOrganizationService iservice, Entity inqueue, MergeService parent, ProcessedDocumentsStats docStat, String impuser)
at AutoMergeService.MergeService.ProcessDocuments(MergeService parent, Int32& pendingRecords)
AUTOMERGEUSC001