How can it be pushed data from LoRa gateway to TTU mote?

Continuing the discussion from How can it be pushed data from LoRa gateway to TTU mote?:

I have no clue, I managed to sent back a confirmation to the gateway but just once, then on the gateway I saw that the status of the message chaged to success, although I haven't been able to repeeat it yet... To do that, I used a code snippet like this one, notice that I am using a different port number to send it since I read it in the command reference from RN2483, but I am not sure this is working because as I have mentioned I managed only once.

if (((String)receivedChars).substring(0,5) == "mac_rx") {
Serial.println("Sever data-> " + (String)receivedChars);
Serial1.write("mac tx uncnf 2 ");//ACK for the server of the data!
return true;
} else
return false;

PS: do you now @scle a better way to check whether mac_rx has arrived?