Use external flash (AT45DB0) with MCUBOOT

I am using nRF Connect SDK v2.2.0 with nRF52810 on a custom board. 
We have included OTA updates in our project, and it works successfully and downloads the firmware via MQTT and writes it using developer.nordicsemi.com/.../dfu_target.html.
Because the internal flash nRF52810 is not enough for us, we want to use the external flash AT45DB0 to store the firmware image.
As an example I used tests\modules\mcuboot\external_flash.
As a result of the build, I get an error:
 
I made a child_image\boards .overlay file:
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/ {
led {
compatible = "gpio-leds";
but_led_1: but_led {
gpios = <&gpio0 12 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
label = "Permission to turn off the device";
};
};
aliases {
mcuboot-led0 = &but_led_1;
};
chosen {
nordic,pm-ext-flash = &at45db0;
};
};
&gpio0 {
status = "okay";
};
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

I made a child mcuboot.config file:
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#
# Copyright (c) 2021 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: LicenseRef-BSD-5-Clause-Nordic
#
CONFIG_MAIN_STACK_SIZE=10240
#CONFIG_PM_PARTITION_SIZE_MCUBOOT=0x10000
#CONFIG_MBEDTLS_CFG_FILE="mcuboot-mbedtls-cfg.h"
CONFIG_MCUBOOT_INDICATION_LED=y
CONFIG_FLASH=y
CONFIG_FPROTECT=y
CONFIG_PM=n
CONFIG_FW_INFO=y
#CONFIG_BOOT_ENCRYPT_EC256=n
#CONFIG_BOOT_ENCRYPT_RSA=n
#CONFIG_BOOT_ENCRYPT_X25519=n
#CONFIG_BOOT_SWAP_SAVE_ENCTLV=n
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Added pm_static.yml file static partition to the root of the project:
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app:
address: 0xc200
end_address: 0xfa000
region: flash_primary
size: 0xede00
external_flash:
address: 0xee000
end_address: 0x800000
region: external_flash
size: 0x712000
littlefs_storage:
address: 0xfa000
end_address: 0x100000
placement:
before:
- end
region: flash_primary
size: 0x6000
mcuboot:
address: 0x0
end_address: 0xc000
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

I spent a lot of time to understand why it doesn't work. I hope you can help me. 
I can provide you with the source files of my project if you need them.