installing larval valet in macOS Heigh Sierra

I'm having issues installing larval valet on macOS Heigh Sierra I already did the following steps.

1. /usr/bin/ruby -e "$(curl -fsSL http://ift.tt/YQTuQh)" - this worked fine

2. brew update - this worked fine

3. brew install homebrew/php/php71 - this worked fine

4. composer global require laravel/valet - this gives me command not found

I know I'm supposed to add it to the path but this command composer global require laravel/valet should work before I add the path

via Chebli Mohamed