I have been trying to send three variables to IFTTT from my ESP32 using Asynchronous Web Server. However, I couldn't set the "URL" that was supposed to be the response that will trigger my IFTTT. Here's is my code:

server.on("/ifttt", HTTP_GET, [](AsyncWebServerRequest *request){

String jsonObject = "{\"value1\":\"" + Global_T + "\"" + ",\"value2\":\"" + Global_H  + "\"" + ",\"value3\":\"" + Global_K +  "\"}";

AsyncWebServerResponse *response = request->beginResponse(200, "application/json", jsonObject);  

response ->addHeader("Host", server_ifttt);
request ->send(response);

It shall get triggered every fixed interval that I have set, and enter here to send it to IFTTT, but this is how it looks like. I not sure where should I add in the "URL" so that the response could be directed to IFTTT.

enter image description here

  • 2
    shouldn't you be using a web client to send data to IFTTT?
    – jsotola
    Commented Apr 16, 2020 at 3:36
  • Sorry, I was kinda new in this. Which means it is impossible for me to send data to IFTTT if I am using Asynchronous Web Server? Commented Apr 16, 2020 at 3:43
  • no, that is not what it means ... you can have web server code, but you also need web client code to connect to the IFTTT server
    – jsotola
    Commented Apr 16, 2020 at 3:48

1 Answer 1


As already said in the comments you need client code - Here are ready to use blocks for your scenario - NEVER use String class if you want to have a stable running IoT device, so define global char arrays (compiled to flash) and keep heap fragmentation at a minimum, The code is commented to get you started, change to your needs:

/* Your constants */
#define READ_THIS_PIN 4
const char MakerIFTTT_Key[] = "r8X-blahblahYourKeyGoesHere";
const char MakerIFTTT_Event[] = "stack_exchange_example";

/* Define global char arrays to get rid of string class */
    char numBuf[20];       // We "just know" this is big enough for (un)signed longs
    char postRequest[256];    // Hand-calculated to be big enough (size to your needs)
/* Helper functions for constructing the POST data
    append a string or int to a buffer, return the resulting end of string */

char *appendStr(char *tempChr, char *s) {
    while ((*tempChr++ = *s++))
    return tempChr-1;

char *appendUl(char *tempChr, unsigned long u) {
    return appendStr(tempChr, ultoa(u, numBuf, 10));
 This is called once per iteration to read the pin
 and send a POST to trigger the IFTTT/Maker event

void updateEvent() {
    WiFiClient client;

    /* Connect to the Maker event server */
    client.connect("maker.ifttt.com", 80);

    /* Construct the POST request */

    postRequest[0] = {'\0'}; /* Reset char array */
    char *p = postRequest;
    p = appendStr(p, "POST /trigger/");
    p = appendStr(p, "MakerIFTTT_Event");
    p = appendStr(p, "/with/key/");
    p = appendStr(p, "MakerIFTTT_Key");
    p = appendStr(p, " HTTP/1.1\r\n");
    p = appendStr(p, "Host: maker.ifttt.com\r\n");
    p = appendStr(p, "Content-Type: application/json\r\n");
    p = appendStr(p, "Content-Length: ");

    /* We need to remember where the content length will go, which is: */
    char *contentLengthHere = p;

    /* It's always two digits, so reserve space for them (the NN) */
    p = appendStr(p, "NN\r\n");

    /* End of headers */
    p = appendStr(p, "\r\n");

    /* Construct the JSON; remember where we started so we will know len */
    char *jsonStart = p;

    // This example reports a pin, uptime, and "hello stack" change to your need */
    p = appendStr(p, "{\"value1\":\"");
    p = appendUl(p, 12);    //analogRead(READ_THIS_PIN));
    p = appendStr(p, "\",\"value2\":\"");
    p = appendUl(p, millis());
    p = appendStr(p, "\",\"value3\":\"");
    p = appendStr(p, "hello, stack!");
    p = appendStr(p, "\"}");

    /* Go back and fill in the JSON length
       we just know this is at most 2 digits (and need to fill in both) */
    uint8_t i = strlen(jsonStart);
    contentLengthHere[0] = '0' + (i/10);
    contentLengthHere[1] = '0' + (i%10);

    // finally we are ready to send the POST to the server!

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