One of Peter's sketches in which he uses JSON to send data to Adafruit IO and receive, parse the response using ArduinoJSON.

sensor.ino

void refresh_readings() {
  float f_temperature;
  float f_humidity;
  float f_pressure;
  float f_altitude;

  digitalWrite(LED_PIN, HIGH);

  postCounter++; // New post, increase the post counter

  f_temperature = bme.readTemperature();
  f_humidity = bme.readHumidity();
  f_pressure = bme.readPressure() / 100.0F;
  f_altitude = bme.readAltitude(SEALEVELPRESSURE_HPA);

  tft.setTextColor(fg, bg);

  tft.loadFont("SansSerif-36"); // Create TTF fonts using instructions at https://pages.uoregon.edu/park/Processing/process5.html

  tft.setRotation(1);

  tft.setCursor(5, 5);
  tft.println("Right now...");
  tft.setTextColor(TFT_YELLOW, bg);

  // Temperature

  tft.fillRect(5, 50, 140, 30, bg);
  tft.setCursor(5, 50);
  tft.print(f_temperature);
  tft.println(" °C");

  // Humidity
  tft.fillRect(5, 90, 130, 30, bg);
  tft.setCursor(5, 90);
  tft.print(f_humidity);
  tft.println(" %");

  // Pressure
  tft.fillRect(5, 130, 200, 30, bg);
  tft.setCursor(5, 130);
  tft.print(f_pressure);
  tft.println(" hPa");

  // Appx altitude
  tft.fillRect(5, 170, 200, 30, bg);
  tft.setCursor(5, 170);
  tft.print(f_altitude);
  tft.println(" m");

  //  // Wifi status
  //  tft.loadFont("NotoSansBold15");
  //  tft.setTextColor(TFT_LIGHTGREY, bg);
  //  tft.fillRect(5, 220, 100, 20, bg);
  //  tft.setCursor(5, 220);
//    tft.print(wl_status_to_string(WiFi.status()));

  client.setCACert(test_root_ca);

  DEBUG_PRINTLN("\nStarting connection to server...");

  if (!client.connect(server, 443))
    DEBUG_PRINTLN("Connection failed!");
  else {
    DEBUG_PRINTLN("Connected to server!");
    // Construct the JSON request:

    // An example of JSON that updates multiple feeds
    String postData = "{ \"feeds\": [ " \
                      "{ \"key\": \"altitude\", " \
                      "  \"value\": \"";

    postData += f_altitude;
    postData += "\" },{ \"key\": \"barpressure\", \"value\": \"";
    postData += f_pressure;
    postData += "\" }, { \"key\": \"humidity\",\"value\": \"";
    postData += f_humidity;
    postData += "\"}, { \"key\": \"temperature\",\"value\": \"";
    postData += f_temperature;
    postData += "\" }]}";
    // Make a HTTP request:
    //    client.println("POST https://io.adafruit.com/api/v2/futureshocked/feeds/lab-environment.testrest/data HTTP/1.0"); // This is the simple case where we post to a single feed.
    client.println("POST https://io.adafruit.com/api/v2/futureshocked/groups/lab-environment/data HTTP/1.0");  // With this, we can post to multiple feeds in a group.
    client.println("Host: io.adafruit.com");
    client.println("Content-Type: application/json");
    client.println("X-AIO-Key: c10ce8eff2ad45c499dd864629ae40e2");
    client.print("Content-Length: ");
    client.println(postData.length());
    //    client.println("Connection: close");
    client.println();
    client.println(postData);


    DEBUG_PRINT("data posting: ");
    DEBUG_PRINTLN(postData);


    while (client.connected()) {
      String line = client.readStringUntil('\n');
      if (line == "\r") {
        DEBUG_PRINTLN("headers received");
        break;
      }
    }
    // if there are incoming bytes available
    // from the server, read them and print them:
    String serverResponse = "";
    while (client.available()) {
      char c = client.read();
      //      Serial.write(c);
      serverResponse += c;
    }

    DEBUG_PRINT("Server response: ");
    DEBUG_PRINTLN(serverResponse);

    client.stop();

    //      // Deserialize the JSON document
    // IT IS NOT NECESSARY TO PARSE THE RESPONCE.
    // IT IS GOOD TO DO SO IF YOU WANT TO CONFIRM THAT WHAT WAS RECORDED BY ADAFRUIT IO IS
    // WHAT YOU SENT.

    const size_t capacity = 2000;
    DynamicJsonDocument doc(capacity);

    //const char* json = "[{\"id\":\"0E3CMHA132FTMAMJ02H6QSYVF4\",\"value\":\"15\",\"feed_id\":1001608,\"feed_key\":\"rest-example.feed1\",\"created_at\":\"2019-02-24T04:13:34Z\",\"location\":null,\"lat\":null,\"lon\":null,\"ele\":null,\"created_epoch\":1550981614,\"expiration\":\"2019-03-26T04:13:34Z\"},{\"id\":\"0E3CMHA132CHVKTDS130N2AP41\",\"value\":\"20\",\"feed_id\":1001609,\"feed_key\":\"rest-example.feed2\",\"created_at\":\"2019-02-24T04:13:34Z\",\"location\":null,\"lat\":null,\"lon\":null,\"ele\":null,\"created_epoch\":1550981614,\"expiration\":\"2019-03-26T04:13:34Z\"}]";
    char json[capacity];

    serverResponse.toCharArray(json, capacity);

    deserializeJson(doc, json);
    JsonObject root_0 = doc[0];
    const char* root_0_id = root_0["id"]; // "0E3J35C42W7Z85D8K8QT00TSDY"
    const char* root_0_value = root_0["value"]; // "112.73"
    long root_0_feed_id = root_0["feed_id"]; // 997698
    const char* root_0_feed_key = root_0["feed_key"]; // "lab-environment.altitude"
    const char* root_0_created_at = root_0["created_at"]; // "2019-03-02T22:59:26Z"
    long root_0_created_epoch = root_0["created_epoch"]; // 1551567566
    const char* root_0_expiration = root_0["expiration"]; // "2019-04-01T22:59:26Z"

    JsonObject root_1 = doc[1];
    const char* root_1_id = root_1["id"]; // "0E3J35C42WQ9J4RZASXD5CDX8E"
    const char* root_1_value = root_1["value"]; // "999.78"
    long root_1_feed_id = root_1["feed_id"]; // 997697
    const char* root_1_feed_key = root_1["feed_key"]; // "lab-environment.barpressure"
    const char* root_1_created_at = root_1["created_at"]; // "2019-03-02T22:59:26Z"
    long root_1_created_epoch = root_1["created_epoch"]; // 1551567566
    const char* root_1_expiration = root_1["expiration"]; // "2019-04-01T22:59:26Z"

    JsonObject root_2 = doc[2];
    const char* root_2_id = root_2["id"]; // "0E3J35C42WHA3G3BNMMGS45J85"
    const char* root_2_value = root_2["value"]; // "52.39"
    long root_2_feed_id = root_2["feed_id"]; // 997696
    const char* root_2_feed_key = root_2["feed_key"]; // "lab-environment.humidity"
    const char* root_2_created_at = root_2["created_at"]; // "2019-03-02T22:59:26Z"
    long root_2_created_epoch = root_2["created_epoch"]; // 1551567566
    const char* root_2_expiration = root_2["expiration"]; // "2019-04-01T22:59:26Z"

    JsonObject root_3 = doc[3];
    const char* root_3_id = root_3["id"]; // "0E3J35C42WS88N6AGBSFMCTQ53"
    const char* root_3_value = root_3["value"]; // "26.93"
    long root_3_feed_id = root_3["feed_id"]; // 997695
    const char* root_3_feed_key = root_3["feed_key"]; // "lab-environment.temperature"
    const char* root_3_created_at = root_3["created_at"]; // "2019-03-02T22:59:26Z"
    long root_3_created_epoch = root_3["created_epoch"]; // 1551567566
    const char* root_3_expiration = root_3["expiration"]; // "2019-04-01T22:59:26Z"

    DEBUG_PRINT("Altitude: ");
    DEBUG_PRINTLN(root_0_value);

    DEBUG_PRINT("barPressure: ");
    DEBUG_PRINTLN(root_1_value);

    DEBUG_PRINT("temperature: ");
    DEBUG_PRINTLN(root_3_value);

    DEBUG_PRINT("Humidity: ");
    DEBUG_PRINTLN(root_2_value);
  }


  heapSize();
  //  // Print memory in an attemp to figure out why wifi is unreliable
  //  tft.fillRect(220, 170, 55, 20, bg);
  //  tft.setCursor(220, 170);
  //  tft.print(esp_get_free_heap_size());
  //
  //  DEBUG_PRINT("Free heap size: ");
  //  DEBUG_PRINTLN(esp_get_free_heap_size());

  postsCounter();
  //  int maxPosts= EEPROM.readInt(0);
  //    if (postCounter > maxPosts)
  //    {
  //      maxPosts = postCounter;
  //      EEPROM.writeInt(0, maxPosts); // Write the new maxPosts in the EEPROM
  //      EEPROM.commit();
  //    }
  //
  //  tft.fillRect(250, 0, 55, 20, bg);
  //  tft.setCursor(250, 0);
  //  tft.print(postCounter);
  //  tft.print("/");
  //  tft.print(EEPROM.readInt(0));

  digitalWrite(LED_PIN, LOW);
}