I measured M-Pesa STK Push polling lag on a real device. The variance will ruin your UX.

Real-device testing of M-Pesa STK Push reveals up to 13x variance in UX response time (3s vs 39s) due to fixed polling schedules colliding with non-deterministic Safaricom callbacks. The key optimization is using WidgetsBindingObserver to trigger an immediate poll when the user returns to the app, reducing perceived wait to 1–2 seconds. A critical undocumented failure mode exists where Safaricom's fire-and-forget callback delivery can silently fail if the server is unreachable, leaving payments stuck in PENDING state.