According to this video, https://www.youtube.com/watch?v=fN_QKOWvG1s , you should be able to flash a sonoff by holding down the button while plugging in electricity, however, when I hold the button down while plugging my sonoff in, it launches as regularly and the led starts blinking green, and then going over to solid green (once it get’s wifi), the same as it does when I connect it without holding the button.
I get this message when I try to flash it: esptool.py v2.0
Connecting………………………__…
A fatal error occurred: Failed to connect to Espressif device: Timed out waiting for packet header