Issue with ArduinoJson on NodeMCU (ESP 8266)

[godestalbin]

Hello,
I have implemented code to call Youtube API. The call works fine and now I wish to deserialize the Json response. My working code is as follow:

#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <WiFiClientSecureBearSSL.h>

// Replace with your network credentials
const char* ssid = "xxxx";
const char* password = "xxxx";

void setup() {
  Serial.begin(115200);
  //Serial.setDebugOutput(true);

  Serial.println();
  Serial.println();
  Serial.println();

  //Connect to Wi-Fi
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  Serial.print("Connecting to WiFi ..");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print('.');
    delay(1000);
  }
}

void loop() {
  // wait for WiFi connection
  if ((WiFi.status() == WL_CONNECTED)) {

    std::unique_ptr<BearSSL::WiFiClientSecure>client(new BearSSL::WiFiClientSecure);

    // Ignore SSL certificate validation
    client->setInsecure();
    
    //create an HTTPClient instance
    HTTPClient https;
    
    //Initializing an HTTPS communication using the secure client
    Serial.print("[HTTPS] begin...\n");
    if (https.begin(*client, "https://www.googleapis.com/youtube/v3/channels?part=statistics&id=xxxx")) {  // HTTPS
      Serial.print("[HTTPS] GET...\n");
      // start connection and send HTTP header
      https.addHeader("X-goog-api-key", "xxxx");
      int httpCode = https.GET();
      // httpCode will be negative on error
      if (httpCode > 0) {
        // HTTP header has been send and Server response header has been handled
        Serial.printf("[HTTPS] GET... code: %d\n", httpCode);   
        // file found at server
        if (httpCode == HTTP_CODE_OK || httpCode == HTTP_CODE_MOVED_PERMANENTLY) {
          Serial.println(https.getString());
        }
      } else {
        Serial.printf("[HTTPS] GET... failed, error: %s\n", https.errorToString(httpCode).c_str());
      }

      https.end();
    } else {
      Serial.printf("[HTTPS] Unable to connect\n");
    }
  }
  Serial.println();
  Serial.println("Waiting 2min before the next round...");
  delay(120000);
}

Here is the response I get with the code above:

{
  "kind": "youtube#channelListResponse",
  "etag": "xxxxxxxxxxxxxxxxxxxxxxxxxxxx",
  "pageInfo": {
    "totalResults": 1,
    "resultsPerPage": 5
  },
  "items": [
    {
      "kind": "youtube#channel",
      "etag": "xxxxxxxxxxxxxxxxxxxxxxxxxxxx",
      "id": "xxxxxxxxxxxxxxxxxxxxxxxxxxxx",
      "statistics": {
        "viewCount": "14025",
        "subscriberCount": "46",
        "hiddenSubscriberCount": false,
        "videoCount": "50"
      }
    }
  ]
}

Thus I added the following code to process the Json response:

#include <ArduinoJson.h>
...
        if (httpCode == HTTP_CODE_OK || httpCode == HTTP_CODE_MOVED_PERMANENTLY) {
          Serial.println(https.getString());
          String payload = https.getString();
          JsonDocument doc;
          DeserializationError error = deserializeJson(doc, payload);
          if (error) {
            Serial.print("deserializeJson() returned ");
            Serial.println(error.c_str());
            return;
          }
          const char* subscriberCount = doc["items"][0]["subscriberCount"]; 
         Serial.print(subscriberCount);
        }

After this change the call does not work anymore.

...[HTTPS] begin...
[HTTPS] GET...
[HTTPS] GET... failed, error: connection failed

I read that it is not a good practice to use String.
I have tried to replace String payload by char payload[500] = "";
This did not help and anyway the type returned by https.getString() is a String.

What could be wrong ?