FOTA doesn't work on nrf5340-DK

Question

Hello,

I am using an nrf5340-DK board and the SDK 1.9.0.

I want integrate the FOTA functionality into the example which was provided by Nordic Semi:

I made 3 modifications according to "FOTA over Blutooth LE" from here:

Modification 1 (main.c)

#include <img_mgmt/img_mgmt.h>
#include <os_mgmt/os_mgmt.h>
#include <mgmt/mcumgr/smp_bt.h>

Modificationn 2 (main.c)

os_mgmt_register_group();
img_mgmt_register_group();
smp_bt_register();

Modification 3 (prj.conf)

CONFIG_MCUMGR=y
CONFIG_MCUMGR_CMD_OS_MGMT=y
CONFIG_MCUMGR_CMD_IMG_MGMT=y
CONFIG_MCUMGR_SMP_BT=y
CONFIG_BOOTLOADER_MCUBOOT=y

Then I create a simple second program which based on "hello_world" example. This program let the LED1 on nrf5340 Board blink let's call it "blinky".

The "blinky" program (app_update.bin) was transfered to the smartphone.

Now the nRF Connect App on the smartphone was started:

DFU was started with "app_update.bin" (blinky) and "Test and Confirm" was selected:

Then I see this for 20 seconds without any progress and "blinky" was not programmed.

I see some similar problems in the DevZone but didn't find the solution for the problem.

What do I have to do to get the FOTA run ?