Describe the final business result.
In a fictional store, one paid order should lead to one fulfillment decision. Identify the records that establish the payment and the record that controls the next task.
Resources / Payment events
What happens if the payment notification arrives twice?
Use one payment path to review the connection between provider activity and application updates.
Review event verification.
Identify how the application verifies the provider notification and associates it with the correct account or transaction. Follow the provider's current integration requirements.
Consider repetition and delay.
A repeated notification should not automatically create another order or repeat fulfillment. Define how processing recognizes work already completed and handles information arriving later.
Separate receipt from completion.
The endpoint may accept an event before a later worker updates the application. Keep enough status information to find and review a failed downstream step.
Test the exception.
Use an authorized isolated environment to repeat an event, delay processing and simulate an update failure. Check the resulting order and records, not only the HTTP response.
Prepare the wider checklist or discuss an integration review.