this my code:

#include <WiFiManager.h>
#include <FirebaseESP32.h>
#include <addons/TokenHelper.h>
#include <addons/RTDBHelper.h>

#define DATABASE_URL ""
#define API_KEY "****"
#define LED1_PIN 12
#define LED2_PIN 14
#define LDR_PIN 36

FirebaseData fbdo;
FirebaseConfig config;
FirebaseAuth auth;

unsigned long sendDataPrevMillis = 0;
bool signupOK = false;
int LdrData = 0;
float voltage = 0.0;

WiFiManager wm;

void setup() {
Serial.begin(115200);
bool res = wm.autoConnect();
if (!res) {
Serial.println("Failed to connect");
} else {
Serial.println("Connected to WiFi");
}

config.api_key = API_KEY;
config.database_url = DATABASE_URL;

if (Firebase.signUp(&config, &auth, "", "")) {
Serial.println("OK connected to Firebase");
signupOK = true;
} else {
Serial.printf("%s\n", config.signer.signupError.message.c_str());
}
config.token_status_callback = tokenStatusCallback;

// Enable TCP KeepAlive
fbdo.keepAlive(5/* idle /, 3 / interval /, 2 / count */);

Firebase.begin(&config, &auth);
Firebase.reconnectWiFi(true);
}

void loop() {
if (Firebase.ready() && signupOK && (millis() - sendDataPrevMillis > 5000 || sendDataPrevMillis == 0)) {
sendDataPrevMillis = millis();

LdrData = analogRead(LDR_PIN);
voltage = (float)analogReadMilliVolts(LDR_PIN) / 1000;

if (Firebase.RTDB.setInt(&fbdo, "Sensor/ldr_data", LdrData)) {
  Serial.println(LdrData);
  Serial.println("--successfully saved to:" + fbdo.dataPath());
} else {
  Serial.println("FAILED:" + fbdo.errorReason());
}
if (Firebase.RTDB.setFloat(&fbdo, "Sensor/voltage", voltage)) {
  Serial.println(LdrData);
  Serial.println("--successfully saved to:" + fbdo.dataPath());
} else {
  Serial.println("FAILED:" + fbdo.errorReason());
}

}
}
this is my serail
Connected to WiFi
OK connected to Firebase
826
--successfully saved to:/Sensor/ldr_data
FAILED:response payload read timed out
816
--successfully saved to:/Sensor/ldr_data
FAILED:response payload read timed out
870
--successfully saved to:/Sensor/ldr_data
FAILED:response payload read timed out
845
--successfully saved to:/Sensor/ldr_data
FAILED:response payload read timed out
873
--successfully saved to:/Sensor/ldr_data
FAILED:response payload read timed out
815
--successfully saved to:/Sensor/ldr_data
FAILED:response payload read timed out
865
--successfully saved to:/Sensor/ldr_data
FAILED:response payload read timed out
749
--successfully saved to:/Sensor/ldr_data
what is the problem,thanks