update your query with this one.
SELECT *
FROM
(SELECT Sales_Doc_Type,
Doc_Date,
Sales_Doc_Num,
Sales_Person_ID,
Customer_Name,
Shipping_Method,
Total,
Subtotal,
xIntFreight,
xSalesmanCost,
SOURCE,
xCommisionPaid,
Payment_Terms
FROM [VISPR].[dbo].[spv3SalesDocument]
WHERE Sales_Doc_Type = 'invoice'
AND Sales_Person_ID = 'xx01'
UNION ALL SELECT Sales_Doc_Type,
Doc_Date,
Sales_Doc_Num,
Sales_Person_ID,
Customer_Name,
Shipping_Method,
Total,
Subtotal,
xIntFreight,
xSalesmanCost,
SOURCE,
xCommisionPaid,
Payment_Terms
FROM [VISPR].[dbo].[spv3SalesDocumentHistory]
WHERE Sales_Doc_Type = 'invoice'
AND Sales_Person_ID = 'xx01'
AND SOURCE NOT IN ('Void')) AS a
INNER JOIN [VISPR].[dbo].[SOP30200] AS b ON a.Sales_Doc_Num = b.SOPNUMBE
AND a.Sales_Doc_Type = b.DOCID
LEFT JOIN [VISPR].[dbo].[spvSalesDocumentTrackingNumber] AS c ON a.Sales_Doc_Num = c.Sales_Doc_Num
AND a.Sales_Doc_Type = c.Sales_Doc_Type
LEFT JOIN
(SELECT DISTINCT x.Sales_Doc_Num,
x.PO_Number,
y.xPOComm
FROM [VISPR].[dbo].[spvSalesLinePO] AS x,
VISPR.dbo.spxPurchaseOrder AS y
WHERE x.PO_Number = y.PO_Number) AS e ON c.Sales_Doc_Num = e.Sales_Doc_Num