Sign up by sending you zip code to the phone number (206) 222-9793. When there is new vaccine appointment availability in your area, you will get a text with a link to schedule your appointment.
Python Flask app hosted by Heroku, has webhooks (endpoints /text and /voice) that receive texts
and calls from Twilio. People sign up, and it adds their phone number and zip code to the Firebase
database. The /notifier endpoint is posted to by the covidwa.com backend, and uses the database
to decide who to send notifications to via text using Twilio.