FIX for macOS/OS X Bootable USB not showing up in Startup Manager

Hi

I have been trying to reinstall macOS on my MacBook Pro 13 (2015) and for reasons I still don't know, the bootable USB I created was not showing up when I booted into the Startup Manager (by holding the option/alt key).

I tried creating the USB via both diskmarkx and Terminal. But neither was helping me. Then I tried several fixes and this one finally solved the problem. For any of you out there facing the same problem, this might help.

Steps :

1. Reset PRAM of your machine by holding option+command+P+R keys together soon after you press the Power button and hear the startup chime.

2. Hold the keys until the grey screen goes off completely (the machine should be restarting).

3. At "this" point, insert the Bootable USB Disk you created and press and hold the option key.

4. Hold the option key until you see the Startup Manager.

Hopefully your USB should be listed as one of the bootable disks in the Startup Manager.