messageDeduplicationId

This parameter applies only to FIFO (first-in-first-out) topics. The MessageDeduplicationId can contain up to 128 alphanumeric characters (a-z, A-Z, 0-9) and punctuation (!"#$%&'()*+,-./:;<=>?@[\]^_{|}~)`.
Every message must have a unique MessageDeduplicationId, which is a token used for deduplication of sent messages within the 5 minute minimum deduplication interval.
The scope of deduplication depends on the FifoThroughputScope attribute, when set to Topic the message deduplication scope is across the entire topic, when set to MessageGroup the message deduplication scope is within each individual message group.
If a message with a particular MessageDeduplicationId is sent successfully, subsequent messages within the deduplication scope and interval, with the same MessageDeduplicationId, are accepted successfully but aren't delivered.
Every message must have a unique MessageDeduplicationId:

You may provide a MessageDeduplicationId explicitly.
If you aren't able to provide a MessageDeduplicationId and you enable ContentBasedDeduplication for your topic, Amazon SNS uses a SHA-256 hash to generate the MessageDeduplicationId using the body of the message (but not the attributes of the message).
If you don't provide a MessageDeduplicationId and the topic doesn't have ContentBasedDeduplication set, the action fails with an error.
If the topic has a ContentBasedDeduplication set, your MessageDeduplicationId overrides the generated one.

When ContentBasedDeduplication is in effect, messages with identical content sent within the deduplication scope and interval are treated as duplicates and only one copy of the message is delivered.
If you send one message with ContentBasedDeduplication enabled, and then another message with a MessageDeduplicationId that is the same as the one generated for the first MessageDeduplicationId, the two messages are treated as duplicates, within the deduplication scope and interval, and only one copy of the message is delivered.