OTA Failed！Failed to Mcumgr DFU: Invalid header magic number

[spring.liu]

why can cause this  problem！ I'm not familiar with NCS OTA

[Einar Thorsrud]

Hi,

The only way I am able to reproduce this is by using an invalid image. Can you clarify which image file you use with nRF Connect? You should use the file called "app_update_bin", and this is found under build/zephyr.