The application cannot write the app_update.bin on Windows.
How do I write with MCUboot & DFU & application?
[Command I tried]
dfu-util --alt 1 --download .\build_nrf52840dk_nrf52840\zephyr\app_update.bin
[output]
dfu-util 0.9
Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2016 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to sourceforge.net/.../
Invalid DFU suffix signature
A valid DFU suffix will be required in a future dfu-util release!!!
No DFU capable USB device available