Want Result from one to many relation table by Group By - sql-server

Question

I would like to get result by "group by" but not luck. I can see other option but looking best perfomance query.
Thanks in Advance !
CREATE TABLE #Invoice (InvoiceId int, InvoiceDate datetime, NetAmount
decimal(18,2))
CREATE TABLE #Payment (PaymentId int, InvoiceId int, PaidAmount
decimal(18,2))
INSERT INTO #Invoice VALUES (101, '20180212', 5000)
INSERT INTO #Invoice VALUES (102, '20180112', 600)
INSERT INTO #Invoice VALUES (103, '20181211', 1800)
INSERT INTO #Invoice VALUES (104, '20180101', 1000)
INSERT INTO #Invoice VALUES (105, '20180212', 7000)
INSERT INTO #Payment VALUES (101,103,1800)
INSERT INTO #Payment VALUES (102,102,500)
INSERT INTO #Payment VALUES (103,101,2000)
INSERT INTO #Payment VALUES (103,101,3000)
Create this query :
SELECT
INV.InvoiceDate,
SUM(Inv.NetAmount) as NetAmount,
SUM(ISNULL(PY.PaidAmount,0)) As PaidAmount
From #Invoice INV
LEFT JOIN #Payment PY
ON PY.InvoiceId = INV.InvoiceId
GROUP BY
INV.InvoiceDate
Get Result :
InvoiceDate NetAmount PaidAmount
2018-01-01 1000.00 0.00
2018-01-12 600.00 500.00
2018-02-12 17000.00 5000.00 ****Issue: Net values should be 12000 not 17000
2018-12-11 1800.00 1800.00
Expected Result :
InvoiceDate NetAmount PaidAmount
2018-01-01 1000.00 0.00
2018-01-12 600.00 500.00
2018-02-12 5000.00 5000.00
2018-12-11 1800.00 1800.00

Answer 1

This assumes that the expected results the OP has provided is wrong. They have the value 5000 for the NetAmount on 20180212, however there are 2 invoices on that date with the values 5000 and 7000, making 12000. If 5000 is correct, we need details on why the value of invoice 105 (7000) is not to be included.
Anyway, on the assumption the expected results is wrong, this gets the result I believe you are looking for:
WITH CTE AS(
SELECT I.InvoiceId,
I.InvoiceDate,
I.NetAmount,
P.PaymentId,
P.PaidAmount,
ROW_NUMBER() OVER (PARTITION BY I.InvoiceId, I.InvoiceDate ORDER BY (SELECT NULL)) AS RN
FROM #Invoice I
LEFT JOIN #Payment P ON I.InvoiceId = P.InvoiceId)
SELECT C.InvoiceDate,
SUM(CASE RN WHEN 1 THEN C.NetAmount END) AS NetAmount,
ISNULL(SUM(C.PaidAmount),0) AS PaidAmount
FROM CTE C
GROUP BY C.InvoiceDate;