How to correctly use external flash storage firmware for Bluetooth mesh dfu distributor

[llly]

I am using ncs2.9.1.

I am currently testing Bluetooth mesh dfu using 54l15dk. Now I want to put the firmware that is ready for updating into the external flash of the distributor, so I enabled the external flash in the distributor example by following the steps below

In sysbuildconf:

In mcuboot.conf:

In app.overlay of mcuboot:

Then download this distributor example to 54l15dk and use the Device Manager app to upload firmware for updates to the distributor.Before using external flash, this upload process can be successfully completed, but after using external flash, an error occurs immediately after the upload starts

[llly]

I also tested it on the NUS example, and as long as the secondary firmware slot is placed in the external flash and DFU is started, the same phenomenon will occur