Add Pagerless to the app
Run it in your repo:
npx pagerless connectAdd Twilio
Paste your Twilio account SID, auth token and number in Alerts. Calls bill on your Twilio account.
Add your phone
Your number for calls, and the iPhone app for the push that comes first.
The call reads a fixed sentence about the problem and asks you to press 1 to acknowledge. If you don't, your backup is next.
Questions
How do I get a phone call when my app is down?
Use an on-call service that calls you. With Pagerless, add the SDK (or run npx pagerless connect), add your Twilio number, and install the iPhone app. If your app goes silent, crash-loops, returns a burst of 5xx errors or payments fail, you get a push, then a call after 5 minutes.