code: func (d *Dispatcher) OnSubmit(channel string, sender uint64, request *orderer.SubmitRequest) error {
  	receiver := d.ChainSelector.ReceiverByChain(channel)
  	if receiver == nil {
  		d.Logger.Warningf("An attempt to submit a transaction to a non existing channel (%s) was made by %d", channel, sender)
  		return errors.Errorf("channel %s doesn't exist", channel)
  	}
  	return receiver.Submit(request, sender)
  }
docs: // OnSubmit notifies the Dispatcher for a reception of a SubmitRequest from a given sender on a given channel