I hadn’t found anything on the internet yet describing how to flash a Sonoff IW100 smart socket, so I thought I’d share my experience.
The RX and TX pins are labeled as they would be conneted to a UART flasher. Wire RX to RX and TX to TX. It’s weird, but that’s how they did it.
Unlike the S31 which has a mechanical button connected to GPIO0, the IW100 has a capacitive button. To short GPIO0 to allow for flashing, use a small F/F jumper to connect GND to TOUCH on the header pins that connect to the front panel capacitive button/LED board. Connect everything together, plug in the USB UART programmer, and quickly upload your firmware.
That is all. Proceed as usual. It is an ESP8285.