Unable to connect dfu

1. Hi currently i am using nrf52840 sdk ver 17.1.0 s140 sd we have added UART in the secure bootloader/ Bootloader_ble_debug  

2. we can able to send multiple bytes once  ie 53 46 30 04 02 01 00 FF 00 00 45 46 on reset of device 

3. we have sending through the func  ret_code_t ret = nrf_drv_uart_tx(&m_uart, data, sizeof(data));

4. while we tried to connect from mobile app but we are unable to connect to dfuTarg 

Logs

<info> app: Inside main
<debug> app: In nrf_bootloader_init
<debug> nrf_dfu_settings: Calling nrf_dfu_settings_init()...
<debug> nrf_dfu_flash: Initializing nrf_fstorage_nvmc backend.
<debug> nrf_dfu_settings: Using settings page.
<debug> nrf_dfu_settings: Copying forbidden parts from backup page.
<debug> nrf_dfu_settings: Destination settings are identical to source, write not needed. Skipping.
<info> nrf_dfu_settings: Backing up settings page to address 0xFE000.
<debug> nrf_dfu_settings: Destination settings are identical to source, write not needed. Skipping.
<debug> app: Enter nrf_bootloader_fw_activate
<info> app: No firmware to activate.
<info> app: Boot validation failed. No valid app to boot.
<debug> app: DFU mode because app is not valid.
<info> nrf_bootloader_wdt: WDT is not enabled
<debug> app: in weak nrf_dfu_init_user
<debug> app: timer_stop (0x200059BC)
<debug> app: timer_activate (0x200059BC)
<info> app: Entering DFU mode.
<debug> app: Initializing transports (found: 2)
<debug> nrf_dfu_ble: Initializing BLE DFU transport
<debug> nrf_dfu_ble: Setting up vector table: 0x000E8000
<debug> nrf_dfu_ble: Enabling SoftDevice.
<debug> nrf_dfu_ble: Configuring BLE stack.
<debug> nrf_dfu_ble: Enabling the BLE stack.
<debug> nrf_dfu_ble: No advertising name found
<debug> nrf_dfu_ble: Using default advertising name
<debug> nrf_dfu_ble: Advertising...
<debug> nrf_dfu_ble: BLE DFU transport initialized.
<debug> nrf_dfu_serial_uart: serial_dfu_transport_init()
<debug> nrf_dfu_serial_uart: serial_dfu_transport_init() completed
<info> nrf_dfu_serial_uart: Sending initial byte 0x24
<debug> nrf_dfu_flash: Initializing nrf_fstorage_sd backend.
<debug> app: Enter main loop

our settings as follows

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