Testing
Test mode works only with numbers you register here, and it makes real requests to IntouchPay's sandbox: the phone rings, and somebody has to approve or decline. Everything else behaves exactly as it does live, because it is the same code and the same provider.
Why the whitelist
Because these are real payment requests, one typo in a test script would send a stranger a prompt for an order that does not exist. Registering the number first makes that impossible by accident. Use numbers you or your team actually answer.
Choosing what happens
On the phone, the way your customers will. Approve the prompt and the payment succeeds; decline it and it fails; ignore it and it sits pending until it expires.
That last one is the case worth spending time on. Leave a prompt unanswered and watch what your code does with a payment.failed that arrives minutes later, after the customer has closed the tab. More on test mode.
No test numbers yet. Add your own phone to start.