This is our app using Fourchette to fork our Heroku app on PR creation.
You can use this as an example of how to use Fourchette and it's callbacks.
You need those environment variable setup, in addition to the ones from Fourchette:
export FOURCHETTE_CLOUDFLARE_EMAIL='email@example.com'
export FOURCHETTE_CLOUDFLARE_API_KEY='your-api-key-here!'
export FOURCHETTE_CLOUDFLARE_DOMAINS='example-qa.com,example-qa-2.com'
# This is the domain you will create subdomain for.