"Blue Pill" is the nickname given to the most popular, ultra-cheap and compact STM32F103 board. It's used to power all of the CannonKeys keyboard kits.
Maybe you've used too much solder on your Blue Pill. Or maybe you didn't use the low profile pins, and can't get the headers to come out. In any case, CannonKeys now offers extras!
Every CannonKeys Blue Pill comes pre-flashed with the bootloader you'll need to use dfu-util to flash it. And our Blue Pills also come with a fixed resistor. Blue Pills you source elsewhere probably won't have the bootloader or the resistor fix!