Execution fails for stored procedure - sql-server

Question

I have an issue with the procedure below.
Error is:
Msg 402, Level 16, State 1, Procedure Get_FormattedBankStatement, Line
87. The data types nvarchar and nvarchar are incompatible in the subtract operator.
USE [K2_Objects]
GO
/****** Object: StoredProcedure [K2RestSrv].[Get_FormattedBankStatement] Script Date: 2/27/2019 5:00:12 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [K2RestSrv].[Get_FormattedBankStatement]
--Declaring input parameter variable
#OpeningBalance Decimal(18,2),
#jsonValue nvarchar(max)
AS
BEGIN
DECLARE
#TotalCount nvarchar(150),
#MinRowNum int, #MaxRowNum int,
#DebitRecord nvarchar(150),
#CreditRecord nvarchar(150),
#NewBalance nvarchar(150),
#PreviousBalance nvarchar(150);
--Creating Temp Table #GetRowID
Create table #GetStatement
(ID int identity(1,1),
PostDate nvarchar(150),
TransDate nvarchar(150),
ValueDate nvarchar(150),
TransID nvarchar(150),
Narration nvarchar(max),
Debit nvarchar(150),
Credit nvarchar(150),
Balance nvarchar(150));
--Inserting into TempTable #GetStatement Temp Table, from the select statement
INSERT INTO #GetStatement
(PostDate,
TransDate,
ValueDate,
TransID,
Narration,
Debit,
Credit,
Balance)
SELECT
max(case when name='post_date' then convert(nvarchar(150),StringValue) else '' end) as [PostDate],
max(case when name='tran_date' then convert(nvarchar(150),StringValue) else '' end) as [TranDate],
max(case when name='value_date' then convert(nvarchar(150),StringValue) else '' end) as [ValueDate],
max(case when name='tran_id' then convert(nvarchar(150),StringValue) else '' end) as [TransID],
max(case when name='narration' then convert(nvarchar(150),StringValue) else '' end) as [Narration],
max(case when name='debit' then convert(nvarchar(150),StringValue) else '' end) as [Debit],
max(case when name='credit' then convert(nvarchar(150),StringValue) else '' end) as [Credit],
max(case when name='balance' then convert(nvarchar(150),StringValue) else '' end) as [Balance]
FROM parseJSON
(
#jsonValue
)
WHERE ValueType IN ('string','real','int','object','array') and Object_ID is NULL
GROUP BY parent_ID;
--Selecting the first and Last RowNum from the TempTable
SET #MinRowNum = (SELECT Min(ID) FROM #GetStatement)
SET #MaxRowNum = (SELECT Max(ID) FROM #GetStatement)
SET #PreviousBalance = #OpeningBalance;
WHILE #MinRowNum < #MaxRowNum
BEGIN
SET #DebitRecord = (SELECT Debit FROM #GetStatement WHERE ID = #MinRowNum);
SET #CreditRecord = (SELECT Credit FROM #GetStatement WHERE ID = #MinRowNum);
SET #NewBalance = (#PreviousBalance - (#DebitRecord + #CreditRecord));
UPDATE #GetStatement SET Balance = #NewBalance WHERE ID = #MinRowNum;
SET #PreviousBalance = (Select Balance from #GetStatement where ID = #MinRowNum);
SET #MinRowNum = (#MinRowNum + 1);
END
Select ID, PostDate,TransDate,ValueDate,TransID,Narration,Debit,Credit,Balance from #GetStatement;
END
GO

Answer 1

Thanks for the support and insights shared.
I was able to overcome the issue, by changing the data type for all areas where I had Decimal(18,2) to money. The variable #OpeningBalance Decimal(18,2) was changed to #OpeningBalance money
Same was done for #DebitRecord, #CreditRecord, #NewBalance, #PreviousBalance
Likewise, 'Coalesce' was used for the calculation of the new balance, by coalescing the PreviousBalance, the CreditRecord, and the DebitRecord.

Answer 2

Change These DECLARES:
#NewBalance nvarchar(150),
#PreviousBalance nvarchar(150);
To
#NewBalance DECIMAL(10,2),
#PreviousBalance DECIMAL(10,2);