WBR2 module with RTL8720CF chip - unable to run simple code

1

Hello,
I have a WBR2 module with RTL8720CF chip, and I would like to play with it using PlatformIO and LibreTiny.
I started with a simple Blinking / Hello world program.

platformio.ini:

[env:generic-rtl8720cf-2mb-992k]
platform = libretiny
board = generic-rtl8720cf-2mb-992k
framework = arduino
upload_port = COM4

main.cpp:

#include <Arduino.h>
pin_size_t led1 = 20;

void setup() {
  pinMode(led1, OUTPUT);
  Serial.begin(115200);
}

void loop() {
  digitalWrite(led1, HIGH);
  delay(500);
  digitalWrite(led1, LOW);
  delay(500);
  Serial.println("Hello world!");
}

Obviously, I have an led on GPIO 20.
I upload the code, everything fine.
But after reboot, the led is not blinking and on serial monitor I have:

== Rtl8710c IoT Platform ==
Chip VID: 5, Ver: 3
ROM Version: v3.0

== Boot Loader ==
Aug 30 2024:04:22:00
[MISC Err]boot_get_load_fw_idx: failed!
[MISC Err]boot_load: Get load FW index err
Boot Load Err!

Any idea what am I doing wrong?

As an info, on the same chip I wrote tasmota-like custom firmware OpenRTL87X0C (GitHub - openshwprojects/OpenBK7231T_App: Open source firmware (Tasmota/Esphome replacement) for BK7231T, BK7231N, BL2028N, T34, XR809, W800/W801, W600/W601, BL602 and LN882H) and it works fine, I also can control the led. So there is no hardware or flashing issue.