Amazon SNS standard topics need duplicate-aware subscribers

Standard SNS topics can deliver messages more than once or out of order, as described in Amazon's SNS overview.

For the SNS integration, send a small sequence with stable business identifiers, then replay an event and reverse two deliveries. The subscriber should preserve a coherent outcome. If ordering requirements lead you toward FIFO features, check their documented scope; a queueing feature is not a blanket guarantee of exactly-once business effects.