Your in-game name (IGN) is the player username for which you will be purchasing the items/ranks. In-game names can not contain especial characters besides the underscore, and are your unique identifier throughout your Minecraft journey. If you are not familiar with your in-game name, you may find it at the top left corner of your minecraft launcher. Alternatively, it is also displayed within the middle section, near the 'Play' button in the Minecraft launcher.