Edited Code

#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <WiFiClient.h>
#define TRIGGER_PIN D1
#define ECHO_PIN D2


  long duration, waterlevel;

  // INSERT WIFI CREDENTIALS
  const char* ssid = "converge-2.4g";
  const char* password = "Sierra911";
  // Your Domain name with URL path or IP address with path
  const char* serverName = "https://us-central1-floodmonitor-474e0.cloudfunctions.net/devices";

void setup() {
  Serial.begin(9600);
  pinMode(TRIGGER_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
    // CONNECTING TO WIFI
  int attempts = 0;
  Serial.print("Connecting to Wi-Fi...");
  while (WiFi.status() != WL_CONNECTED && attempts < 10) {
    attempts++;
    WiFi.begin(ssid, password);
    delay(1000);
    Serial.print(".");
}
}

void loop() {
  //INSERT DEVICEID AND LATITUDE AND LONGITUDE (NO LAT AND LONG SINCE NO GPS MODULE IS USED)
    if (WiFi.status() == WL_CONNECTED) {
    Serial.println("Still Connected");
  } else {

    Serial.println("Reconnecting");
      int attempts = 0;
  Serial.print("Connecting to Wi-Fi...");
  while (WiFi.status() != WL_CONNECTED && attempts < 10) {
    attempts++;
    WiFi.begin(ssid, password);
    delay(1000);
    Serial.print(".");
    }

  }

  int deviceID = 1;
  String lat = "14.5784832";
  String longitude = "121.1367424";
  String flooded = "";

  // GETTING LEVEL OF FLOOD
  waterlevel = ultrasonic_distance();
  Serial.print("Flood Level: ");
  Serial.println(waterlevel);

  //  CHANGE VALUE TO DETERMINE HOW HIGH IF ITS FLOODED OR NOT
  bool flood = (waterlevel >= 50);
  if (flood == 1) {
  Serial.println("The Area is Flooded.");
  flooded = "true";
  } else {
  Serial.println("The Area is not Flooded.");
    flooded = "false";
  }


  HTTPClient http;
  WiFiClientSecure client;
  client.setInsecure();

  // Your Domain name with URL path or IP address with path
  http.begin(client,serverName);


  // HTTP POST (SEND JSON TO DATABASE)
  http.addHeader("Content-Type", "application/json");
  String payload = "{\"deviceId\":\"" + String(deviceID) + "\",\"lat\":\"" + String(lat) + "\",\"long\":\"" + String(longitude) + "\",\"waterLevel\":\"" + String(waterlevel) + "\",\"flooded\":\"" + String(flooded) + "\"}"; ;
  int httpResponseCode = http.POST(payload);

  // IF RESPONSE CODE IS LESS THAN 0 THEN DATA IS NOT BEING SENT
  Serial.print("HTTP Response code: ");
  Serial.println(httpResponseCode);

  //Serial.print("Data Being Sent: ");
  // CREATE A STRING TO SEND TO THE ARDUINO
  String SMS = "Device ID: "+String(deviceID) +" Water Level : "+String(waterlevel)+ " Area: Dito Flooded: " + String(flooded);
  // PUT DATA IN SERIAL MONITOR TO BE SENT TO ARDUINO TO BE SENT IN AN SMS
  Serial.println(SMS);

  //STARTING TO SEND SMS
  Serial.print("\r");
  delay(10000);
  Serial.print("AT+CMGF=1\r");
  delay(1000);
  /*Replace XXXXXXXXXX to 10 digit mobile number &  ZZ to 2 digit country code*/
  Serial.print("AT+CMGS=\"09171367340\"\r");

  //The text of the message to be sent.
  Serial.print(String(SMS));
  delay(1000);
  Serial.write(0x1A);
  delay(1000);

  // Free resources
  http.end();

  // Wait for 1 second
  delay(30000);
}

long ultrasonic_distance() {
  // Send a 10 microsecond pulse to the trigger pin
  // HC-SR04 VCC -> NodeMCU 5V
  // HC-SR04 GND -> NodeMCU GND
  // HC-SR04 TRIG -> NodeMCU D1
  // HC-SR04 ECHO -> NodeMCU D2
  digitalWrite(TRIGGER_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIGGER_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIGGER_PIN, LOW);

  // Measure the duration of the echo pulse
  duration = pulseIn(ECHO_PIN, HIGH);

  // Convert the duration to a distance
  waterlevel = duration * 0.034 / 2;

  // Return the distance measurement
  return waterlevel;
}