Hi,
I have completed all steps in the example at the following link https://devzone.nordicsemi.com/b/blog/posts/getting-started-with-nordics-secure-dfu-bootloader and all works OK.
Without modification i have compiled the Buttonles DFU application example, created a zip file and sucessfully loaded it onto the device. However the only service is a LED Button Service and was expecting A DFU service. Can action DFU by pressing Button 4 and Reset but need a buttonless service. Does the example application code require further configuration to operate?