Series 3 — Solution · Paper 1
A Payment
Rachel makes preserves. On Saturday mornings she sells them at a farmers’ market in the town where she lives. She has a regular spot, a folding table, and a laminated card that she props against the front of her display.
The card has a code printed on it.
David is at the market with his daughter. She picks up a jar of raspberry jam and shows it to him. £4.50. He takes out his phone, opens his camera, and points it at the card on Rachel’s table.
His phone shows him a screen. Rachel’s stall name. £4.50. A box where he types the amount — he enters 4.50, the screen shows £4.50. A button that says Pay.
He presses it.
His bank asks him to confirm. He uses his fingerprint. The confirmation takes about two seconds.
His phone shows a receipt. Rachel’s stall name, £4.50, the time, a reference number.
Rachel’s phone, in her pocket, buzzes. She takes it out. £4.50 received. She puts it back.
She hands the jar to his daughter.
The whole exchange, from David pointing his phone at the card to Rachel handing over the jam, takes less than thirty seconds. Neither of them has touched a card terminal. Neither of them has typed an account number. David has not downloaded an app. Rachel has not rented any equipment.
What has happened, underneath the thirty seconds:
David’s bank received an instruction to pay £4.50 to Rachel’s account. It verified that David authorised the instruction — the fingerprint confirmation — and that the account it was paying into was registered with a licensed payment provider. It moved the money. The whole process completed before David had finished putting his phone in his pocket.
Rachel’s account received £4.50. Her payment provider sent her the notification. The transaction appears in her records with the reference, the time, and David’s payment provider’s confirmation that the funds have cleared.
Both of them have a record of the same transaction. The records agree. There is nothing to reconcile, nothing to chase, nothing to dispute.
The card on Rachel’s table cost her nothing to produce and nothing to maintain. It works for every customer who has a smartphone, regardless of which bank they use or which payment app they prefer. It works in the rain. It works when Rachel is busy with another customer and can’t touch anything. It works identically for the first customer of the morning and the last.
When Rachel packs up and goes home, she takes the card with her. Next Saturday it will be on the table again, and it will work in exactly the same way, for exactly the same reason.
The code on the card does not change. What changes, each Saturday, is that Rachel is there to hand over the jam.