Stored procedure not accepting any value - sql-server

Question

I have written a stored procedure based on a set of process, I'm just passing a single parameter as input to the procedure but it seems it is not taking the value. But when I give input value instead of parameter in the procedure it is working.
There is no mistake in the flow of process, but seems something missing in the procedure syntax end.
below is the stored procedure I used.
ALTER PROCEDURE [TransferIn]
#ponumber NVARCHAR = NULL
AS
BEGIN
--step 1 Delete Temp Pur_ID
IF EXISTS (
SELECT TABLE_NAME
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME = 'Pur_ID_IN')
DROP TABLE Pur_ID_IN;
-- =============================================
--step 2 select PO Number
--IF #ponumber IS NOT NULL
SELECT
ponumber, id
INTO Pur_ID_IN
FROM purchaseorder
WHERE potype IN (2, 4)
AND status = 0
AND ponumber = #ponumber;
-- =============================================
--step 3
--delete Temp. Tabel P_Test20_12_IN
IF EXISTS (
SELECT TABLE_NAME
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME = 'P_Test20_12_IN')
DROP TABLE P_Test20_12_IN;
-- =============================================
-- step 4 (Insert Data For Invoice To Temp Tabel After Group )
SELECT
ItemDescription, PurchaseOrderID,
SUM(QuantityOrdered) AS QuantityOrdered,
itemid, Price
INTO P_Test20_12_IN
FROM PurchaseOrderEntry
WHERE PurchaseOrderID IN (SELECT id FROM Pur_ID_IN)
GROUP BY
ItemDescription, StoreID, PurchaseOrderID,
itemid, Price;
--order by 3
-- =============================================
-- step 5 Delete Record From PurchaseOrderEntry
DELETE PurchaseOrderEntry
FROM PurchaseOrderEntry
WHERE PurchaseOrderID IN (SELECT id FROM Pur_ID_IN);
-- =============================================
INSERT INTO [W07].[dbo].[PurchaseOrderEntry] ([ItemDescription], [LastUpdated], [PurchaseOrderID], [QuantityOrdered], [ItemID], [Price])
SELECT
[ItemDescription],
GETDATE() AS [LastUpdated],
[PurchaseOrderID], [QuantityOrdered],
[ItemID], [Price]
FROM
P_Test20_12_IN;
END

Answer 1

Problem is
#ponumber nvarchar = null
change it to
#ponumber nvarchar(max) = null
Note:If you do NOT specify the size(char, nchar, varchar, nvarchar),
sql server will default to 1 character.

Answer 2

ALTER PROCEDURE [TransferIn]
(
#ponumber NVARCHAR(100)
)
AS BEGIN
SET NOCOUNT ON
IF OBJECT_ID('tempdb.dbo.#temp') IS NOT NULL
DROP TABLE #temp
CREATE TABLE #temp (id INT PRIMARY KEY)
INSERT INTO #temp (id)
SELECT /*DISTINCT*/ id
FROM dbo.purchaseorder
WHERE potype IN (2, 4)
AND [status] = 0
AND ponumber = #ponumber
IF OBJECT_ID('tempdb.dbo.#temp2') IS NOT NULL
DROP TABLE #temp2
SELECT ItemDescription,
PurchaseOrderID,
SUM(QuantityOrdered) AS QuantityOrdered,
itemid,
Price
INTO #temp2
FROM PurchaseOrderEntry
WHERE PurchaseOrderID IN (SELECT * FROM #temp)
GROUP BY ItemDescription,
StoreID, --?
PurchaseOrderID,
itemid,
Price;
DELETE PurchaseOrderEntry
FROM PurchaseOrderEntry
WHERE PurchaseOrderID IN (SELECT * FROM #temp)
INSERT INTO [W07].[dbo].[PurchaseOrderEntry] ([ItemDescription], [LastUpdated], [PurchaseOrderID], [QuantityOrdered], [ItemID], [Price])
SELECT [ItemDescription],
GETDATE() AS [LastUpdated],
[PurchaseOrderID],
[QuantityOrdered],
[ItemID],
[Price]
FROM #temp2
END