Serial LTE Modem FOTA download error

[Umer Mahmood]

After triggering FOTA download, following are the logs from nrf9160:
without CONFIG_DOWNLOAD_CLIENT_HTTP_FRAG_SIZE_1024=y in prj.conf

00> [00:03:30.366,455] <inf> download_client: Downloaded 2048/316987 bytes (0%)
00> [00:03:30.367,065] <err> dfu_target: No supported image type found
00> [00:03:30.367,523] <err> fota_download: Unknown image type
00> [00:03:30.368,011] <inf> download_client: Fragment refused, download stopped.
00> [00:03:30.368,957] <dbg> slm_uart_handler: slm_uart_tx_write: TX
00>                                            0d 0a 23 58 46 4f 54 41  3a 20 30 2c 31 2c 32 0d |..#XFOTA : 0,1,2.
00>                                            0a                                               |.                

with CONFIG_DOWNLOAD_CLIENT_HTTP_FRAG_SIZE_1024=y in prj.conf

00> [00:02:30.750,152] <inf> download_client: Downloaded 1024/316987 bytes (0%)
00> [00:02:30.750,701] <err> dfu_target: No supported image type found
00> [00:02:30.751,190] <err> fota_download: Unknown image type
00> [00:02:30.751,708] <inf> download_client: Fragment refused, download stopped.

I have not enabled FULL FOTA. I am testing FOTA for application update. 
NCS SDK: 2.5.1

Rest of the prj.conf related to FOTA looks like this:

# FOTA
CONFIG_HTTP_PARSER_URL=y
CONFIG_FOTA_DOWNLOAD=y
CONFIG_FOTA_DOWNLOAD_PROGRESS_EVT=y
CONFIG_DFU_TARGET=y
CONFIG_DOWNLOAD_CLIENT=y
CONFIG_DOWNLOAD_CLIENT_STACK_SIZE=4096
CONFIG_DOWNLOAD_CLIENT_MAX_FILENAME_SIZE=2048
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_IMG_MANAGER=y
CONFIG_DOWNLOAD_CLIENT_HTTP_FRAG_SIZE_1024=y

# FLASH
CONFIG_FLASH=n
CONFIG_FLASH_PAGE_LAYOUT=n
CONFIG_FLASH_MAP=n
CONFIG_STREAM_FLASH=n
CONFIG_MPU_ALLOW_FLASH_WRITE=n
CONFIG_IMG_ERASE_PROGRESSIVELY=n

[Umer Mahmood]

problem resolved after adding 

CONFIG_DFU_TARGET_MCUBOOT=y

had to enable other settings as well, final configuration looks like this:

# FOTA
CONFIG_HTTP_PARSER_URL=y
CONFIG_FOTA_DOWNLOAD=y
CONFIG_FOTA_DOWNLOAD_PROGRESS_EVT=y
CONFIG_DFU_TARGET=y
CONFIG_DOWNLOAD_CLIENT=y
CONFIG_DOWNLOAD_CLIENT_STACK_SIZE=4096
CONFIG_DOWNLOAD_CLIENT_MAX_FILENAME_SIZE=2048
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_IMG_MANAGER=y
CONFIG_DFU_TARGET_MCUBOOT=y

# FLASH
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_FLASH_MAP=y
CONFIG_STREAM_FLASH=y
CONFIG_MPU_ALLOW_FLASH_WRITE=y
CONFIG_IMG_ERASE_PROGRESSIVELY=y

# Settings
CONFIG_SETTINGS=y
CONFIG_SETTINGS_FCB=y
CONFIG_FCB=y