The bank never answered. Did the money move?

transcript

Meera pays 1,999 rupees by UPI. Thirty seconds pass. No answer. Did the money move? Guess wrong, and she's charged twice.

The obvious move: no reply, so mark it failed. But people retry when they see failed. If the money moved, that's a double charge.

So silence gets its own state. Not failed. Unknown. Meera sees: confirming your payment. Don't pay again. Then a status check, a late callback or a file decides. Authorised, or failed. Money moved after we said failed? Late success. Captured, or refunded automatically.

Now resolve it. Thirty seconds, no callback. Unknown. At 90 seconds, ask: what happened to T1? Pending. At 180, ask again. But here's the catch. NPCI allows only three checks, 90 seconds apart. All pending? The next day's settlement file is the final word. T1 in it? The money moved.

Is this rare? Suppose 1 percent of UPI payments have no answer at 30 seconds. At peak, that's 50 new unknowns a second. About 13,500 at once. Unknown isn't an error path. It's a normal state.

Never turn silence into an answer. The bank that never answered isn't the bug. The bug is the system that guessed.

Full breakdown in the lecture.