MQTT Mosquitto and two ESP8266 - arduino

Question

My problem:
I have a Raspberry Pi, and I have installed the Mosquitto MQTT broker on it. My objective is to make 2 MQTT clients communicate over the Mosquitto broker, so I have installed the code below on two ESP8266 (WeMos D1 mini)
and I have created this MQTT command: mosquitto_pub -h 192.168.1.20 -t /wassim/led -m "on".
So, when I connect only one ESP client, I see the message "on" in the serial monitor. But when I connect the second ESP client, I can't see any message on the serial monitor... (But if on the terminal of the Raspberry, then I can see everything. On the clients I can't see anything). The code:
#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <MQTTClient.h>
float temp;
float lm;
String aw="";
const char* host = "192.168.1.20";
const char* ssid = "THOMSON1121";
const char* password = "Wassim";
WiFiClient net;
MQTTClient mqtt;
void connect();
void setup() {
Serial.begin(115200);
Serial.println();
Serial.println("Booting...");
WiFi.mode(WIFI_AP_STA);
WiFi.begin(ssid, password);
mqtt.begin(host, net);
connect();
if(mqtt.subscribe("/wassim/led")) {
Serial.println("Subscription Valid !");
}
Serial.println("Setup completed...");
}
void loop() {
if (!mqtt.connected()) {
connect();
}
mqtt.loop();
delay(3000);
}
void connect() {
while(WiFi.waitForConnectResult() != WL_CONNECTED) {
WiFi.begin(ssid, password);
Serial.println("WiFi connection failed. Retry.");
}
Serial.print("Wifi connection successful - IP-Address: ");
Serial.println(WiFi.localIP());
while (!mqtt.connect(host)) {
Serial.print(".");
}
Serial.println("MQTT connected!");
}
void messageReceived(String topic, String payload, char * bytes, unsigned int length) {
Serial.print("incoming: ");
Serial.print(topic);
Serial.print(" - ");
Serial.print(payload);
Serial.println();
}
The change from one client to another is if(mqtt.subscribe("/wassim/tmp")).

Answer 1

MQTT is a 'message bus' application....in order to have multiple 'subscribers' receive the same message that is being put on the bus by a 'publisher', they both have to subscribe to the same topic...or at least enough of the topic + wildcard...in order to get sent that published message. You only have one of your two clients listening to the topic that your 'mosquitto_pub' command is sending out. For it to receive, you either specify the full topic (mqtt.subscribe("/wassim/led")), or a wildcard to pick up all the 'wassim' messages sent out (mqtt.subscribe("/wassim/#")).