Olá, quero enviar um json simples utilizando a biblioteca arduinoJson6 utilizando o method POST da biblioteca ESP8266HTTPClient.h.

#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <ArduinoJson.h>

const char* ssid = "ctc";
const char* password = "ctcwebapnew";

void setup () {

Serial.begin(115200);
WiFi.begin(ssid, password);

while (WiFi.status() != WL_CONNECTED) {

delay(1000);
Serial.println("Connecting..");

}

}

void loop() {

if (WiFi.status() == WL_CONNECTED) { //Check WiFi connection status

HTTPClient http; //Declare object of class HTTPClient

http.begin("http://192.168.1.18:5000/postjson"); //Specify request destination
http.addHeader("Content-Type", "application/json"); //Specify content-type header
//http.addHeader("Content-Type", "text/plain"); //Specify content-type header

const int capacity = 6; //JSON_OBJECT_SIZE(3);
StaticJsonDocument<capacity> doc;

doc["teste1"] = 1;
doc["teste2"] = 2;
doc["teste3"] = 3;

//***** aqui dá o erro! *****
int httpCode = http.POST(doc); //Send the request
String payload = http.getString(); //Get the response payload

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

http.end(); //Close connection

} else {

Serial.println("ERRO AO CONECTAR AO WIFI!");

}

delay(5000); //Send a request every 5 seconds

}