The slack app for this function is located at: https://api.slack.com/apps/AMKJDBHLL
It was created by following this tutorial: https://cloud.google.com/functions/docs/tutorials/slack
First you'll need to login:
npx gcloud auth login
You'll be taken to a browser window, where you'll need to login to the GCloud account.
After logging in, deploy the app using the following command:
npx gcloud functions deploy promoter-mailgun-stats --runtime nodejs8 --trigger-http
The latest code should now be up.