The Bluetooth pairing feature is part of the DFU (Device Firmware Updater)  and the DFU is only present in .hex files that were generated using the MakeCode editor. 

The MicroPython language does not have enough memory for Bluetooth use, so the Bluetooth is disabled, and no DFU code is present in any .hex file generated by the Python Editor

Using the MakeCode Editor, write a simple program and flash the resulting .hex file onto your micro:bit using a USB lead. This will restore the DFU firmware upgrader, and pairing mode will work again. 

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