Here is my code:

// define radio stuff
#define MY_RADIO_NRF24
#define MY_BAUD_RATE 9600
#define MY_DEBUG    // Enables debug messages in the serial log
//#define MY_NODE_ID 13

// add signing stuff
//#define MY_SIGNING_SOFT // Enables software signing
//#define MY_SIGNING_REQUEST_SIGNATURES // Always request signing from gateway
//#define MY_SIGNING_SOFT_RANDOMSEED_PIN 7 // floating pin for randomness
//#define MY_DEBUG_VERBOSE_SIGNING

#include <EEPROM.h>
#include <SPI.h>
#include <MyConfig.h>
#include <MySensors.h>
#include <Vcc.h>
#include <RCSwitch.h>

const long RECEIVER_PIN = 0;
const long SENDER_PIN = 7;
const long DEBOUNCE = 500;
const long CHILD_RECEIVER = 0;
const long CHILD_SENDER = 1;


RCSwitch wirelessSwitch = RCSwitch();


void presentation()
{
  sendSketchInfo("433 Wireless Gateway", "29062017");

  present(CHILD_RECEIVER, S_INFO); // able to receive text
  present(CHILD_SENDER, S_INFO); // able to send text
}

void setup() {
  wirelessSwitch.enableReceive(RECEIVER_PIN); // Receiver on interrupt 0 => that is pin #2
  wirelessSwitch.enableTransmit(SENDER_PIN);  // Sender on pin 7
  Serial.println("Started listening on pin 2 for incoming 433Mhz messages");
}

void loop() {
  if (wirelessSwitch.available()) {
  	// for testing
    //output(wirelessSwitch.getReceivedValue(), wirelessSwitch.getReceivedBitlength(), wirelessSwitch.getReceivedDelay(), wirelessSwitch.getReceivedRawdata(),wirelessSwitch.getReceivedProtocol());

    unsigned long received_val = wirelessSwitch.getReceivedValue();

    Serial.print("Received 433Mhz message: ");
    Serial.println(received_val);

    send(MyMessage(CHILD_RECEIVER, V_TEXT).set(received_val));

    // software debounce
    wait(DEBOUNCE);
    wirelessSwitch.resetAvailable();
  }
}

void receive(const MyMessage &message) {
  Serial.print("Sensor: "); Serial.print(message.sensor); Serial.print(", Message: "); Serial.println(message.getString()); 
  if (message.type == V_TEXT) { 
    if (message.sensor == CHILD_SENDER) {
      Serial.println("Sending message via 433Mhz");
      char * messageContent = strdup(message.getString());
      wirelessSwitch.send(messageContent);
    }
  }
}

On the domoticz side I have a piece of lua code (using dzVents) that just copies the receiver value to the sender

return {
        active = true,
        on = {
            '433Receiver'
        },
        execute = function(domoticz, sensor)

            domoticz.log("Received from gateway " .. sensor.state)
            -- check sensor values 
            domoticz.devices['433Sender'].updateText(sensor.state)
        end
    }

and its working in the domoticz ui... Is this a domoticz error or am I missing something in my code?