Payment Lab · Flow Explorer
What each system knows when a transaction takes an unexpected path.
A host can approve a payment while the terminal still shows UNKNOWN. Choose a scenario, step through the events, and inspect what Terminal, Middleware, Host, and Merchant honestly know at each moment. Illustrative simulation using synthetic data; retry and reversal behavior varies by scheme, acquirer, host, terminal, and contract.
Host approves; terminal never observes the response.
- 00+0ms▶···
TXN CREATED
Terminal creates sale
- 01+120ms▶◀··
REQUEST SENT
Request sent to middleware
- 02+240ms·▶◀·
REQUEST RECEIVED
Middleware forwards request
- 03+360ms·◀▶·
HOST APPROVED
Host approves
- 04+480ms◀▶··
RESPONSE SENT
Middleware sends final response
- 05+600ms····
MESSAGE LOST
Terminal response lost
- 06+720ms····
TIMEOUT
Terminal timeout
- 07+840ms▶◀··
STATUS QUERY
Terminal queries status
- 08+960ms◀▶··
STORED RESPONSE REPLAYED
Stored response replayed
- 09+1080ms▶◀··
ACK SENT
Terminal ACK dispatched
- 10+1200ms▶◀··
ACK RECEIVED
Middleware records ACK
What is known now?
- HostNONE
- MiddlewareCREATED
- TerminalPENDING
- DeliveryNOT SENT
- Merchant visibilityPENDING
- Financial dispositionNOT DETERMINED
Response to terminal lost
TXN CREATED
Terminal creates sale
A sale request is composed on the terminal. Nothing else has happened yet — no request in flight, no host contact.