What happens if I have a duplicated message ID in the SQSBatchItemFailure

It will cause that message to be retried.

When Lambda processes a batch of SQS messages and encounters an error processing one of the messages, it will report the failed message ID back to SQS. If the same message ID is reported multiple times, SQS will keep returning that message to Lambda for processing.

Some key points:

Lambda follows an at-least-once delivery model for SQS integration. Messages may be delivered multiple times on failure or timeout.

Your Lambda function code needs to be idempotent to handle duplicate message delivery without errors.

Tracking state to avoid duplicate processing on retries is recommended, such as with DynamoDB.

Messages will be sent to the dead letter queue if the max receive count is exceeded due to failures.

Check your Lambda function code and logs to ensure errors are not falsely reported for messages.