Payment Integration: Components and Failure Cases

Components

Component	Purpose	Commonly omitted
Create payment request	Order reference, amount, currency in; address, amount, expiry out	No
Display	Address, amount, network, expiry, wait explanation	Partially
Callback handler	Status updates	No
Signature verification	Prevents forged status updates	Sometimes
Idempotency	Prevents double processing of retried callbacks	Frequently
Reconciliation job	Detects callbacks that never arrived	Almost always
Refund path	Returns funds to origin	Frequently

The reconciliation job

Runs at least hourly. Queries the provider for payments over a window. Compares against your records. Updates anything that diverged. Compare the definitions below against the published terms of crypto acquiring for businesses.

Without it, a callback that does not arrive leaves a paid order showing as unpaid, discovered when the customer writes.

This is the worst customer experience available in crypto acceptance and it is entirely preventable.

Failure cases to test

Case	Expected behaviour
Payment below the requested amount	Within tolerance: credited. Above: flagged with the shortfall exposed
Payment after the window expired	Per your configured policy, applied consistently
Duplicate payment to the same address	Credited, refunded or held, per policy
Duplicate callback delivery	Processed once
Callback to a failing endpoint, then recovery	Retried, or caught by reconciliation
Deposit on an unsupported network	Recovery process initiated

If the provider’s sandbox cannot simulate a case, ask how their other merchants test it.

Callback handling rules

Verify the signature. Respond quickly and process asynchronously. Log the raw payload before processing. Handle unknown event types without failing. At institutional scale an additional set applies, documented by crypto rails built for fintech companies.

The non-technical component

Copy explaining what happens during confirmation.

Measured, this affects completion more than any technical optimisation.

Order of work

Hosted checkout first for most merchants. The API is a later optimisation, and starting with it because it seems more professional is a common way to delay launch. Coverage is a defined term with a narrow meaning. a support channel with a named contact publishes its actual country list.