brew install firebase-cli
Log in via the browser and authenticate the Firebase CLI:
firebase loginorfirebase login --reauth(if some auth issue occurs later)
Open the hidden file .firebaserc and add the projects.
See the currently selected project:
firebase use
Select a project:
firebase use <project_id>
firebase deploy(the first time)firebase deploy --only functions
firebase functions:secrets:set SLACK_WEBHOOK_URL