Messages can be deduplicated to prevent duplicate messages from being sent. When a duplicate message is detected, it is accepted by QStash but not enqueued. This can be useful when the connection between your service and QStash fails, and you never receive the acknowledgement. You can simply retry publishing and can be sure that the message will enqueued only once. In case a message is a duplicate, we will accept the request and return the messageID of the existing message. The only difference will be the response status code. We’ll send HTTP 202 Accepted code in case of a duplicate message.

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Deduplication ID

To deduplicate a message, you can send the Upstash-Deduplication-Id header when publishing the message. 
curl -XPOST \
    -H 'Authorization: Bearer XXX' \
    -H "Content-type: application/json" \
    -H "Upstash-Deduplication-Id: abcdef" \
    -d '{ "hello": "world" }' \
    'https://qstash.upstash.io/v2/publish/https://my-api..."'

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Content Based Deduplication

If you want to deduplicate messages automatically, you can set the Upstash-Content-Based-Deduplication header to true. 
curl -XPOST \
    -H 'Authorization: Bearer XXX' \
    -H "Content-type: application/json" \
    -H "Upstash-Content-Based-Deduplication: true" \
    -d '{ "hello": "world" }' \
    'https://qstash.upstash.io/v2/publish/...'
Content based deduplication creates a unique deduplication ID for the message based on the following fields:
  • Destination: The topic or endpoint you are publishing the message to.
  • Body: The body of the message.
  • Header: This includes the Content-Type header and all headers, that you forwarded with the Upstash-Forward- prefix. See custom HTTP headers section.