Install game-porting-toolkit Error !

1. arch -x86_64 ./brew -v install game-porting-toolkit

Error: 
Formulae found in multiple taps:
       * apple/apple/game-porting-toolkit
       * gcenx/apple/game-porting-toolkit
Please use the fully-qualified name (e.g. apple/apple/game-porting-toolkit) to refer to a specific formula.

FIX:
# untap the other source
arch -x86_64 ./brew untap gcenx/homebrew-apple # ./brew is your x86 brew bianry path

# rerun the tap command
arch -x86_64 ./brew -v install game-porting-toolkit. # need to add arch -x86_64