Hello
If you are using a KW45 chip for the first time received from the factory, The NBU is mandatory for flashing and testing BLE examples, because the memories integrated in the NBU consist of Bluetooth LE controller stack and radio drivers.
For a KW45 chip that it's not the KW45B41Z-EVK, it is necessary to program the fuse first, download the NBU firmware and finally download the CM33 firmware.
Could you help us confirm; What it is the intended use for this KW45 chip, operating the same as the KW45B41Z-EVK or as custom operation?
For more information about this please refer to Application Note AN14003 Programming the KW45 flash for Application and Radio firmware, I would recommend checking on Chapter 2 Figure 2 the Process flow used, this for a visual image on how the NBU its operating in the process.
Best Regards
Luis