https://devzone.nordicsemi.com/f/nordic-q-a/20966/dfu-bootloader-fails-second-updateI have a created a bootloader using the bootloader_secure example in SDK 12.1. Using my own public-private key pair I&#39;ve created two zip files, signed with nrfutil, one with the application firmware and one with the bootloader itself (if I ever want toen-USTelligent Community 13Fri, 31 Mar 2017 08:42:38 GMThttps://devzone.nordicsemi.com/thread/81935?ContentTypeID=1Fri, 31 Mar 2017 08:42:38 GMT137ad170-7792-4731-bb38-c0d22fbe4515:b49af02d-8115-42b2-9e30-6c73a86b6da2Eddie<p>Yes, the version checking is probably causing this. I thought that version 0xffff was used as wildcard and would be ignored, clearly it isn&#39;t. Not sure where I read that or where I got that from.</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/81934?ContentTypeID=1Thu, 30 Mar 2017 16:01:42 GMT137ad170-7792-4731-bb38-c0d22fbe4515:2e627830-b814-4fe5-bdda-5d4b8182131dMoritz<p>The bootloader update is only allowed when the version-number of the update is higher than the version on device. So for the first update you should set e.g. --bootloader-version 0x01 and for the second-update --bootloader-version 0x02. Of course you could also remove this check in the SDK&#39;s DFU code.</p> <p>Something similar I experienced in the past, but this doesn&#39;t seem to be your issue: If you do a combined Bootloader+SD+App-update on multiple devices without leaving the DFU screen, then the iOS nrf Toolbox App fails doing the bootloader update on the second device. Don&#39;t know if this bug still exists, but as said this is most likely not your problem.</p><div style="clear:both;"></div>