🛒 Retail & E-commerce · Sequence

Checkout and Payment Sequence

What happens when a shopper clicks Pay: stock is reserved, the payment is authorised, the order is created and stock is released again if payment fails.

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Drawing diagram…

What this diagram shows

Stock is reserved before payment so items don't oversell
Failed payments release the reserved stock
Confirmation email is sent only after the order is saved

Prompt used

Checkout sequence: the shopper clicks Pay, the order service asks the inventory service to reserve stock, then calls the payment service which charges the payment gateway. On success the order is saved as confirmed and a confirmation email is sent. On failure the reserved stock is released and the shopper sees a retry option.

Mermaid code

sequenceDiagram
  actor S as Shopper
  participant W as Web Store
  participant O as Order Service
  participant I as Inventory Service
  participant P as Payment Service
  participant G as Payment Gateway
  S->>W: Click Pay
  W->>O: Place order
  O->>I: Reserve stock
  I-->>O: Reserved
  O->>P: Charge Rs 2,499
  P->>G: Authorise
  alt Payment succeeds
    G-->>P: Success
    P-->>O: Paid
    O->>O: Save order as confirmed
    O-->>W: Order confirmed
    O-)S: Confirmation email
  else Payment fails
    G-->>P: Declined
    P-->>O: Failed
    O->>I: Release stock
    O-->>W: Show retry option
  end

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