Transaction Broker - Error - 'you cannot add detail lines to transactions that are no longer batched'

This is a common error in Transaction Broker.
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This means that one of the references / header / invoice number / order number that you are trying to import (source file), already exist in your Dimensions data.
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As the same reference exists in Dimensions (cannot have duplicates), that already been posted and not flagged as batched.
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Please check the invoice number / order number / header reference in your source data and you will find that the same already exists / has been posted in Dimensions. Once you change the reference for that record in your source data, you will then be able to import successfully using transaction broker.