https://devzone.nordicsemi.com/f/nordic-q-a/25101/how-to-debug-app-bootloaderHi all, I have sent an application ZIP OTA and performed DFU, the log: ... &lt;debug&gt; app: All flash operations have completed. &lt;debug&gt; app: Starting reset timer. &lt;debug&gt; app: Attempting to reset the device. &lt;debug&gt; nrf_sdh_soc: In nrf_dfu_transports_closeen-USTelligent Community 13Tue, 12 Sep 2017 09:05:13 GMThttps://devzone.nordicsemi.com/thread/98852?ContentTypeID=1Tue, 12 Sep 2017 09:05:13 GMT137ad170-7792-4731-bb38-c0d22fbe4515:14cc0ec3-d6ea-454a-8648-9d8e5302717bPetter Myhre<p>0x00000004 is NRF_ERROR_NO_MEM.</p> <p>You can try to increase NRF_SDH_BLE_VS_UUID_COUNT. This may give you a new error, because the SoftDevice will require more RAM. Have a look at nrf_sdh_ble_enable().</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/98851?ContentTypeID=1Tue, 12 Sep 2017 02:00:09 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f9a1ece7-c921-4c9b-b9e2-0267ee8141f2parco<p>I have debugged it by merging the application.hex with the settings.hex, and overwriting the debug&#39;s target hex with that merged file. Then simply started debugging.</p> <p>Also, I have narrowed the problem down to sd_ble_uuid_vs_add returning error 4.</p><div style="clear:both;"></div>