An Alternative ID - or Alt ID - is another ID that we use to correlate Agent Events when a common Correlation ID is not available.
Where a business object from one system is available at multiple monitoring points, we can use Alt IDs to correlate Agent events where a common Correlation ID is not available. This is done by mapping the source business object identifier to one of the Alt IDs.
Alt IDs need only be unique for the duration of the correlation window (defined within the Flow).