alguna vez tuve ese detalle, lo que pasa que al hacer match con inner Join en esos documentos se repiten los numeros de documentos como doc entrys y viceversa.
checa esta estructura haber si te funciona.
SELECT
-- T1."SeriesName" as "Serie",
CASE T2."InvType"
WHEN 13 THEN 'Factura'
WHEN 14 THEN 'N.Credito'
END as "Docto",
CASE T2."InvType"
WHEN 13 THEN (SELECT A."DocNum" FROM OINV A WHERE A."DocEntry"=T2."DocEntry")
WHEN 14 THEN (SELECT A."DocNum" FROM ORIN A WHERE A."DocEntry"=T2."DocEntry")
END as "#SAP",
CASE T2."InvType"
WHEN 13 THEN (SELECT A."DocDate" FROM OINV A WHERE A."DocEntry"=T2."DocEntry")
WHEN 14 THEN (SELECT A."DocDate" FROM ORIN A WHERE A."DocEntry"=T2."DocEntry")
END as "Fecha Docto.",
T0."DocNum" as "No. Pago",
T0."CardCode" as "Código Cliente",
T0."CardName" as "Nombre Cliente",
CASE T2."InvType"
WHEN 13 THEN (SELECT A."DocTotal" FROM OINV A WHERE A."DocEntry"=T2."DocEntry")
WHEN 14 THEN (SELECT A."DocTotal" FROM ORIN A WHERE A."DocEntry"=T2."DocEntry")*-1
END as "Imp.Docto",
CASE T2."InvType"
WHEN 13 THEN T2."SumApplied"
WHEN 14 THEN T2."SumApplied"*-1
END as "Imp.Aplicado",
CASE T2."InvType"
WHEN 13 THEN (SELECT A."PaidToDate" FROM OINV A WHERE A."DocEntry"=T2."DocEntry")
WHEN 14 THEN (SELECT A."PaidToDate" FROM ORIN A WHERE A."DocEntry"=T2."DocEntry")*-1
END as "Tot.Pagado",
T0."CashSum" as "Efectivo",
T0."CheckSum" as "Cheque",
T0."TrsfrSum" as "Transf",
T0."DocTotal" as "Total",
T0."DocDate" as "Fecha",
T4."SlpName"||' '||T4."Memo"
FROM ORCT T0
INNER JOIN NNM1 T1 ON T0."Series" = T1."Series"
LEFT JOIN RCT2 T2 ON T0."DocEntry" = T2."DocNum"
LEFT JOIN OCRD T3 ON T0."CardCode" = T3."CardCode"
LEFT JOIN OSLP T4 ON T3."SlpCode" = T4."SlpCode"
WHERE T0."Canceled" = 'N' and T0."DocDate" between [%0] and [%1]
ORDER BY T0."DocNum"