Esp8266 no serial prints / connecting to WiFi and MQTT Broker problem

Projects Programming
3 
void setup() {
  Serial.begin(115200);
  #if defined(ESP8266)
  S.begin(9600, SWSERIAL_8N1);
  mb.begin( & S, DE_RE);
  mb.master();
  #endif

  setup_wifi();
  client.setServer(mqtt_server, 8883);
  client.setCallback(callback);
}