may be they dont have any payment history. in that case, make it like
SELECT SUM(Table_NEWDR_Payment_History.Amount_Received) AS [Total Amount Received], Table_NEW_DR.ReferenceNumber
FROM Table_NEW_DR LEFT JOIN
Table_NEWDR_Payment_History ON Table_NEW_DR.ReferenceNumber = Table_NEWDR_Payment_History.ReferenceNumber
GROUP BY Table_NEW_DR.ReferenceNumber, Table_NEWDR_Payment_History.ReferenceNumber
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SQL Server MVP
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