The pinout is clearly marked on the board - 5 pins. VCC3.3, GND, GPIO0,TX,RX. Need to ground GPIO0 then connect VCC,GND,TX,RX to serial. Unground GPIO0 and proceed with flashing. (The on-board button is NOT connected to GPIO0. Need to ground that specific pin in the 5-pin pinout to get into flash mode)
Button 1 being inverted was causing tasmota to factory reset. Changed to non-inverted. This may be incorrect for older boards?