Thank you to Ahmed and Reuven for the tip on WriteResult:: getFailedStorageApiInserts.
When I tried to get the successful inserts through the Storage Write API, I received an error message saying that "Retrieving successful inserts is only supported for streaming inserts. Make sure withSuccessfulInsertsPropagation is correctly configured for BigQueryIO.Write object." Did I make a mistake, or is there a reason why this is not possible? I tried setting triggeringFrequency + numStorageWriteApiStreams as required by Storage Write, and I tried to set successfulInsertsPropagation as directed in the error message.
