Review on 🔌 Enhanced Songhe Mega2560 + WiFi R3: Mega NodeMCU with USB-TTL CH340G, ATmega2560, ESP8266 32Mb Memory – Arduino & WeMos ESP8266 Compatible by Greg Baker

It took me hours of reading and research to get it working. I would make another start if the seller included the documentation and that the ESP8266 comes with updated software. I had to update the AT version to make it work and most online examples I found use Serial1 (pins 18 and 19), the board hardware comes for Serial 3 (pins 14 and 15), switch 1 and switch 2 should be set to the correct potion, it was awful figuring all this out without documentation but I got it working.