WhatsApp appointment reminders Diagram

Privacy

Patients, appointments and payments live only on the phone; the server never sees names or phone numbers
The server only receives the push endpoint, a random id per appointment and the reminder time
The push is empty: the text is built on the phone, with an option to hide names
Optional fingerprint or PIN lock (WebAuthn)

From alert to message

The cron sends a single push per device and retries a minute later if it fails
The notification opens the "Send reminder" sheet in the app, not wa.me: Android won't pass that link to WhatsApp from a notification
No paid API: the therapist just taps send in WhatsApp

Why a fixed URL

The data, the installed app and the push subscription are tied to the domain
A tunnel with a changing URL would lose all of it; Funnel gives fixed HTTPS without opening ports
The app never reloads by itself: a "New version available · Update" bar

Deployment and testing

One Docker container with a healthcheck, published only through the tunnel
The same API code also runs on Cloudflare Workers + D1
End-to-end test with Playwright and a real push through FCM
JSON backup from the app, with a reminder after 14 days