What prevents a single payment intent from creating duplicates in error?

The option that prevents a single payment intent from creating duplicates is the Idempotency Key. When an Idempotency Key is included in a payment request, it ensures that even if the same request is sent multiple times (for example, due to network errors or user actions), only one payment will be processed. Each Idempotency Key is unique to a specific transaction and, when the same key is used for subsequent requests, Stripe recognizes that the request has already been processed. Thus, it does not create a new payment intent or duplicate the transaction, effectively ensuring that the operation is performed only once.

In contrast, a Unique Transaction Identifier might refer to an identifier for keeping track of various transactions, but it does not inherently prevent duplicates as a functional feature. The Payment Processing Algorithm relates more to how payments are handled internally rather than preventing duplicates. Similarly, a Session Token does not serve the specific purpose of managing idempotency for payment intents. The crucial role of the Idempotency Key in creating unique transactions by preventing duplicates is what makes it the correct answer in this context.