Error received when flashing custom Nordic application to DVK-BL65x: SVCALL(SD_SOFTDEVICE_ENABLE, uint32_t, sd_softdevice_enable(nrf_clock_lf_cfg_t const * p_clock_lf_cfg, nrf_fault_handler_t fault_handler)); Programming custom Nordic App to DVK-BL65x

This error indicates and issue with the clock source referenced in your code. We recommend referencing the appropriate Application Note for Using the DVK-BL65x and Nordic SDK linked below:

As noted in the Application Note, by default the DVK-BL65x uses the on-chip RC oscillator as its clock source, as opposed to Nordic's development kit or dongle which use an external crystal. The difference in oscillator source should therefore be reflected in the SDK as shown Application Note. Alternatively, you can connect an external crystal as per BL65x DVK User Guide