how i connect on https://www.googleapis.com/identitytoolkit/v3/relyingparty ?

I tried the code below but to no avail!
Using the same parameters postman has successfully returned!
Every help is welcome!

// Load Wi-Fi library
#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>

void setup()
{
HTTPClient http;
http.begin("https://www.googleapis.com");
http.addHeader("Content-Type", "application/x-www-form-urlencoded");

int httpCode = http.POST("/identitytoolkit/v3/relyingparty/verifyPassword?key=xxxxx&email=zzz@gyyyy.com.xx&password=12345&returnSecureToken=true");

String payload = http.getString(); //Get the response payload

Serial.println("--------------");
Serial.println(httpCode); //Print HTTP return code
Serial.println("--------------");
Serial.println(payload); //Print request response payload

http.end(); //Close connection

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