code: async def send_offnetwork_invitation(
              self, send_offnetwork_invitation_request
      ):
          
          response = hangouts_pb2.SendOffnetworkInvitationResponse()
          await self._pb_request('devices/sendoffnetworkinvitation',
                                 send_offnetwork_invitation_request,
                                 response)
          return response
docs: Send an email to invite a non-Google contact to Hangouts.