changes in Bootloader- saving image in external flash and transferring in internal via Bootloader

[Anil Snadhan]

Hi , I am using ZEPHYR rtos , and using the internal bootloader and its working fine and there are two images but now my code size has increased and i can not store 2 images in internal flash  so have to do implementation of saving the image to external flash and after validation move to internal flash ,what changes i require to make in zephyr bootloader to add external flash code(SPI) and  using only 1 image in bootloader 

[Anil Snadhan]

I have done the implementation but facing this issue

what can cause this issue also attaching my project files

00> *** Booting Zephyr Otonga_nrf52833.dtsS build v2.4.99-ncs1 ***usb_cdc_acm_log_recovery.conf

00> I: Starting bootloader 00> W: Failed reading sectors; BOOT_MAX_IMG_SECTORS=512 - too small?

00>E: Image in the primary slot is not valid!

00> E: Unable to find bootable image

also 

[Hung Bui]

Have you flashed MCUBoot ? 
What did you flash to the app primary slot configured by MCUBoot ? 

[Anil Snadhan]

yeah i have flashed the mcuboot, image first is my application previously my code has 2 images in internal flash and it was working fine ,the as my code size  increased mode the i used external flash for image -1 and internal flash for image -0 and this error start showing can you guiide what more changes are required to made in bootloader code for it