How to flash Sonoff/Esp8266

Flash Sonoff over-the-air

If you can't get the web UI to show, then pair it to Ewelink and delete it again. Sonoff can be slow to start up the web interface, be patient. ¹
The Firmware file cannot be bigger than 500k ¹
As for the web server, make sure it'll take any host name and support partial requests (HTTP 206) : ²

python3 -m pip install --user esptool
python3 -m esptool --chip esp8266 -p /dev/ttyUSB0 write_flash 0x0 ./firmware_file.bin