Double Purchase Protection

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Double Purchase Protection helps prevent accidental duplicate charges when a user submits the same purchase request multiple times. This is commonly caused by retries, double-clicks, or parallel requests.

What it does

• Blocks duplicate purchases for the same user and content when protection is enabled.
• Returns a conflict response instead of creating a second confirmed charge.
• Stores a failed transaction for audit and support visibility.

How it works

The system uses a combination of identifiers to determine duplicates:

1. Unique identifiers
   We use clientTransactionId, phone, and content to detect duplicate transactions.

2. Duplicate check logic
   A payment is flagged as a duplicate if either of the following combinations match a previous transaction:

3. If clientTransactionId exists, match on clientTransactionId, phone, and content
4. Else match on phone and content

How transactions are handled

For every transaction attempt, the system performs these checks:

1. Check for unique clientTransactionId
   If a transaction comes with a unique clientTransactionId, it is treated as a new transaction.

2. Combination check
   If the combination of phone and content, or clientTransactionId, phone, and content matches any previous transaction, the request is identified as a duplicate.

Error response (when blocked)

The API responds with a conflict status and Zlick error code:

{
  "statusCode": 409,
  "error": "DuplicatePaymentBlockedError",
  "message": "Transaction blocked due to duplicate transaction protection. Check your records for a recent, successful payment before retrying.",
  "zlickErrorCode": "ZLICK16",
  "info": {
    "existingTransactionId": "...",
    "existingTransactionState": "confirmed",
    "existingTransactionAmount": 499,
    "existingTransactionDate": "2026-01-26T12:34:56.789Z",
    "doublePurchaseProtectionEnabled": true
  }
}