The customer really did buy the same thing twice. How do I prove it?

Distinct order numbers, timestamps, separate confirmation emails, and two deliveries or two service records make the case. Two authorization codes for two approvals also strongly indicate two intentional purchases.

I already refunded the duplicate. Why did a P08 still arrive?

The dispute and your refund likely crossed. Respond with the refund reference and date; Amex resolves the case once it verifies the credit posted.

American Express · Processing Errors

Reason code P08: Duplicate Charge

P08 covers a single transaction billed to the cardmember more than once. Two identical charges on one card in a short window are presumed duplicates unless the merchant proves each was a distinct purchase.

Issuer filing window

typically 120 days from the charge date

Merchant response window

typically 20 days to respond

Why P08 chargebacks happen

A timeout during checkout led the customer or staff to submit the payment again, and both attempts captured.
A settlement batch was transmitted twice after an error message that looked like a failure.
Two identical orders (same item, same amount, same day) were genuine but appear duplicated on the statement.
A gateway retry mechanism resubmitted a charge that had actually succeeded the first time.

How to fight a P08 chargeback

Prove distinctness: supply separate invoices, order numbers, item details, and delivery records for each charge.
Show unique authorization approval codes for each transaction, since true duplicates often share or lack them.
If one charge is genuinely a duplicate, refund it immediately and document the credit in your response so the case closes cleanly.
Provide session or terminal logs demonstrating two intentional purchase events where the amounts merely coincide.

How to prevent P08 chargebacks

Implement idempotency keys on payment requests so retries can never create a second capture.
Disable double-click submission and show clear in-progress states at checkout.
Alert on same-card, same-amount captures within a short window and hold the second for review.
Verify batch transmission status with your processor before ever resending a file.

Frequently asked questions

The customer really did buy the same thing twice. How do I prove it?: Distinct order numbers, timestamps, separate confirmation emails, and two deliveries or two service records make the case. Two authorization codes for two approvals also strongly indicate two intentional purchases.
I already refunded the duplicate. Why did a P08 still arrive?: The dispute and your refund likely crossed. Respond with the refund reference and date; Amex resolves the case once it verifies the credit posted.

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