flashing pico with stm32loader.py

starting to work with a pico attached to USB.

o connected WebIDE to pico and did a reset() and disconnected

 _____                 _
|   __|___ ___ ___ _ _|_|___ ___
|   __|_ -| . |  _| | | |   | . |
|_____|___|  _|_| |___|_|_|_|___|
          |_| http://espruino.com
 1v80 Copyright 2015 G.Williams

o next step: update to 1v87

python -V
Python 2.7.10

python stm32loader.py -k -p /dev/cu.usbmodem1421 espruino_1v87_espruino_1r3.bin 
Can't init. Ensure BOOT0=1, BOOT1=0, and reset device
Traceback (most recent call last):
  File "stm32loader.py", line 554, in <module>
    bootversion = cmd.cmdGet()
  File "stm32loader.py", line 140, in cmdGet
    if self.cmdGeneric(0x00):
  File "stm32loader.py", line 137, in cmdGeneric
    return self._wait_for_ack(hex(cmd))
  File "stm32loader.py", line 101, in _wait_for_ack
    raise CmdException("Unrecognised response 0x%x to %s" % (ask, info))
__main__.CmdException: Unrecognised response 0xff to 0x0

what is missing ?