trying to switch input on my speakers via infrared using web browser but i have issue getting it working ived tested the IR code with 
https://github.com/wemos/D1_mini_Examples/blob/master/examples/04.Shields/IR_Controller_Shield/IRsend/IRsend.ino

and it works that way, but when i try to code it together with the web server, i get nothing, can someone explain to me what's wrong in my code? the webserver works fine, its the IR part i dont fully understand why its not working

#include &lt;i18n.h&gt;
#include "ESP8266WiFi.h"
#include "ESP8266WebServer.h"
#include &lt;IRremoteESP8266.h&gt;
#include &lt;IRsend.h&gt;
ESP8266WebServer server(80);

void setup() {
  Serial.begin(115200, SERIAL_8N1, SERIAL_TX_ONLY);
  WiFi.begin("net", "pass");  //Connect to the WiFi network

  while (WiFi.status() != WL_CONNECTED) {  //Wait for connection

    delay(500);
    Serial.println("Waiting to connect…");

  }

  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());  //Print the local IP

  server.on("/on", []() {   //Define the handling function for the path

    server.send(200, "text / plain", "Switching to USB input");
    #define IR_LED D3  
    IRsend irsend(IR_LED);  // Set the GPIO to be used to sending the message.
    uint16_t rawData[71] = {8992, 4494,  574, 558,  572, 558,  574, 558,  574, 558,  574, 558,  572, 558,  572, 556,  572, 1660,  572, 1658,  574, 1658,  574, 1658,  574, 1660,  574, 1660,  574, 1660,  574, 1658,  602, 528,  574, 558,  574, 1658,  576, 556,  574, 556,  574, 1660,  574, 556,  574, 554,  574, 554,  574, 1658,  574, 556,  574, 1656,  576, 1658,  576, 556,  574, 1658,  576, 1656,  576, 1658,  576, 39978,  8994, 2256,  578};
    irsend.begin();

  });

  server.on("/", handleRootPath);    //Associate the handler function to the path
  server.begin();                    //Start the server
  Serial.println("Server listening");

}

void loop() {

  server.handleClient();         //Handling of incoming requests

}

void handleRootPath() {            //Handler for the rooth path

  server.send(200, "text/plain", "NinjaLights");

}
Look at your code. You set up the sender, define the data and then never use it:

server.on("/on", []() {   //Define the handling function for the path
    server.send(200, "text / plain", "Switching to USB input");
    #define IR_LED D3  
    IRsend irsend(IR_LED);  // Set the GPIO to be used to sending the message.
    uint16_t rawData[71] = {8992, 4494,  574, 558,  572, 558,  574, 558,  574, 558,  574, 558,  572, 558,  572, 556,  572, 1660,  572, 1658,  574, 1658,  574, 1658,  574, 1660,  574, 1660,  574, 1660,  574, 1658,  602, 528,  574, 558,  574, 1658,  576, 556,  574, 556,  574, 1660,  574, 556,  574, 554,  574, 554,  574, 1658,  574, 556,  574, 1656,  576, 1658,  576, 556,  574, 1658,  576, 1656,  576, 1658,  576, 39978,  8994, 2256,  578};
    irsend.begin();

  });


You need to add a call to irsend.SendRaw() to actually send the data - otherwise you didn't actually do anything.

So your code would look like:

server.on("/on", []() {   //Define the handling function for the path
    server.send(200, "text / plain", "Switching to USB input");
    #define IR_LED D3  
    IRsend irsend(IR_LED);  // Set the GPIO to be used to sending the message.
    uint16_t rawData[71] = {8992, 4494,  574, 558,  572, 558,  574, 558,  574, 558,  574, 558,  572, 558,  572, 556,  572, 1660,  572, 1658,  574, 1658,  574, 1658,  574, 1660,  574, 1660,  574, 1660,  574, 1658,  602, 528,  574, 558,  574, 1658,  576, 556,  574, 556,  574, 1660,  574, 556,  574, 554,  574, 554,  574, 1658,  574, 556,  574, 1656,  576, 1658,  576, 556,  574, 1658,  576, 1656,  576, 1658,  576, 39978,  8994, 2256,  578};
    irsend.begin();

    irsend.sendRaw(rawData, 71, KHZ);
  });


You'll need to replace KHZ with the frequency the remote you're trying to replicate uses, otherwise it still won't work.