Contactless Payment at a Vending Machine

Sequence Diagram

Contactless Payment at a Vending MachineContactless Payment at a Vending MachineUserVending MachineCard.PhonePayment GatewayIssuing BankUserUserVending MachineVending MachineCard/Phone(NFC Device)Card/Phone(NFC Device)Payment GatewayPayment GatewayIssuing BankIssuing BankItem SelectionSelect itemCalculate total amountDisplay total & prompt for paymentPayment InitiationTap card/phone on NFC readerTransmit payment informationCapture payment dataAuthorization ProcessRequest Authorization(amount, card details)Route transaction detailsCheck account funds& fraud indicatorsalt[Transaction Approved]Authorization ApprovedForward approval responsePayment Success FlowDisplay "Payment Successful"Activate dispensing mechanismDispense selected itemItem dispensedTransaction Complete(finalize fund transfer)[Transaction Declined]Authorization DeclinedForward decline responsePayment Failure FlowDisplay "Payment Failed"Cancel transaction

Description

A sequence diagram illustrating the rapid, automated communication that happens when a user pays for an item at a modern vending machine using contactless payment (NFC card or mobile phone).

Key Participants

  • User: The customer making the purchase
  • Vending Machine: The smart vending device with NFC capability
  • Card/Phone (NFC Device): The contactless payment method (credit card or mobile device)
  • Payment Gateway: The intermediary processing service that handles transaction routing
  • Issuing Bank: The bank that issued the payment card and holds the customer's account

Process Flow Breakdown

1. Item Selection Phase

The interaction begins when the user selects their desired item from the vending machine interface. The machine calculates the total cost and displays it along with a payment prompt.

2. Payment Initiation

The user initiates payment by tapping their NFC-enabled card or mobile device on the machine's contactless reader. The NFC device transmits encrypted payment information to the vending machine, which captures and processes this data.

3. Authorization Request

The vending machine sends an authorization request containing the transaction amount and encrypted card details to the payment gateway. The gateway acts as a secure intermediary, routing the transaction details to the appropriate issuing bank for validation.

4. Bank Validation

The issuing bank performs multiple security checks including:

  • Account balance verification
  • Fraud detection algorithms
  • Card validity confirmation
  • Transaction limit verification

5. Response Handling

Based on the validation results, the bank sends either an approval or decline response back through the payment gateway to the vending machine.

6A. Success Path

If approved, the vending machine displays a success message, activates its dispensing mechanism to release the selected item, and sends a transaction completion signal to finalize the fund transfer.

6B. Failure Path

If declined, the machine displays a failure message and cancels the transaction, returning to the initial state.

Technical Considerations

Security Features:

  • End-to-end encryption of payment data
  • Tokenization to protect sensitive card information
  • Real-time fraud detection
  • Secure communication protocols between all participants

Performance Aspects:

  • Near-instantaneous NFC communication (< 100ms)
  • Typical authorization time of 2-5 seconds
  • Automated dispensing mechanism activation
  • Real-time transaction processing

Error Handling:

  • Network timeout management
  • Payment decline scenarios
  • Mechanical failure contingencies
  • Transaction rollback capabilities

Real-World Applications

This diagram pattern applies to various contactless payment scenarios including public transportation, parking meters, retail kiosks, and other automated payment systems. The sequence demonstrates modern payment infrastructure's ability to handle secure, rapid transactions with minimal user interaction.