InvalidHeaderMagic error when calling let package = try McuMgrPackage(from: savedUrl)

[ljunquera]

I am getting InvalidHeaderMagic error when calling

let package = try McuMgrPackage(from: savedUrl)

In version 1.7.3 which I need to use because it supports Swift5.

I saw in this post the comment:

So the 'invalid header magic' means the Data is not signed. So, you were maybe trying to DFU Data from a debug build, not Release. This is why it probably worked with your file instead of the Data bytes directly.

but I am using the app_update.bin from the build/zephyr file and have this in the prj.conf:

# Enable MCUboot and FOTA
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU=y
CONFIG_MCUBOOT_SIGNATURE_KEY_FILE="mcuboot/root-rsa-2048.pem"

I also saw the post How to generate imageData where the error was referenced, but that seems like a customization of the code.