Following the instructions outputs, among others, a file named bootloader_espruino_2vXX.XX_mdbt42q.hex as well as dfu_settings.hex.
I tried flashing bootloader_espruino_2xXX.XX_mdbt42q.hex to the target with nrfGo Studio, with no success.
What is the correct procedure to flash the bootloader?
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
You need the bootloader and softdevice in the hex file as well as the actual firmware. Best bet is to build your own - just follow the instructions on https://github.com/espruino/Espruino/blob/master/README_Building.md and use PUCKJS or MDBT42Q as the board name