Get field value for child document
get/documents/{objectTypeName}/{documentId}/children/{childDocType}/{childDocId}/fields/{fieldName}
Gets a representation of a field value for a child document. If the field is configured for masking, and if the requesting user is authorized to reveal the value of the masked field, the raw unmasked value of the field is returned. If the field is configured for masking and the requesting user is not authorized to reveal the value of the masked field, the result is an error.