nrfutil device program - Unable to open device

[smmx]

Hello

I have just received thingy:91 x to start learning nrf platform. Unfortunately it's not all smooth. I am trying to do flash Blank application. It builds fine but then when I try to flash thingy I get  error (see below).

Maybe I missed something important, but I did follow all the docs

$ nrfutil device program --firmware build/dfu_application.zip --serial-number THINGY91X_46EEE9... --traits mcuBoot --x-family nrf91 --core Application
[00:00:00] ------ 0% [THINGY91X_46EEE9...] Failed, Unable to open device
Error: One or more program tasks failed:
* THINGY91X_46EEE9...: Unable to open device (Generic)

$ nrfutil device list
THINGY91X_46EEE9...
Product Thingy:91 X UART
Ports /dev/ttyACM0, vcom: 0
/dev/ttyACM1, vcom: 1
Traits mcuBoot, nordicUsb, serialPorts, usb, modem

Supported devices found: 1

$ sudo lsof | grep ttyACM
shows no /dev/tty is open

I did add myself to dialout group as well

[Distromel]

I'm just starting with Thingh91X. I've followed the fundamentals tutorial without problems.

Now I'm trying to generate a multithreading project but when I'm going to program the device I get the following error:

PS C:\myfw\ncsfund\workspace\threads> nrfutil device program --firmware dfu_application.zip --serial-number THINGY91X_5FBB616A50D
Error: Firmware does not exist dfu_application.zip