flashing pico with stm32loader.py

using a official build

240488 13 Sep 11:44 espruino_1v87_espruino_1r3.bin

python stm32loader.py -p /dev/cu.usbmodem1421 -evw espruino_1v87_espruino_1r3.bin 
Reading data from espruino_1v87_espruino_1r3.bin
Bootloader version 0x30
Chip id 0x414, STM32F1, performance, high-density
Global mass erase; this may take a while
Writing 240488 bytes to start address 0x8000000
Write 256 bytes at 0x8000000
........
Read 256 bytes at 0x803AB00
Verification FAILED
240488 vs 240488
0x1: 0xc0 vs 0x80
.......
0x3fff: 0xe0 vs 0xff

tried a different usb cable - same result