DFRobot:esp8266 "Error: 13 INTERNAL: Server responded with: 502 Bad Gateway"

Good morning, 

I'm trying to use My board Firebeetle ESP32/8266. I have followed the wiki guide: “FireBeetle_ESP8266_IOT_Microcontroller_SKU__DFR0489-DFRobot”, so with Arduino IDE 2.x, I'm trying to set the development environment, but when I select the DFRobot FireBeetle-ESP3266 board (2.3.3, but I tried also others minor versions), the Arduino logs say:
 

With the URL https://downloadcd.dfrobot.com.cn/boards/package_DFRobot_index.json I have this output:

Downloading packages
DFRobot:[email protected]
DFRobot:[email protected]
Failed to install platform: 'DFRobot:esp8266:2.3.3'.
Error: 13 INTERNAL: Server responded with: 502 Bad Gateway

Instead, with this URL https://raw.githubusercontent.com/DFRobot/FireBeetle-ESP8266/master/package_firebeetle8266_index.json the output is:

Failed to install platform: 'FireBeetle-ESP8266:2.3.1'. 9 FAILED_PRECONDITION: Platform 'firebeetle8266:[email protected]' not found: getting tool dependencies for platform firebeetle8266:[email protected]: tool mkspiffs not found

I understand that there is a network problem between the package server and my Arduino IDE. 
Can I use another Additional Boards Manager URL?

Best regards