SAP B1 Transaction - Checking same prices between ORDR and OINV

Hello Guys,

I'm trying to validate the price of Invoice to be the same as Sales Order to prevent an user to make changes in moment of add Invoice document. So I made this code in transaction notification to block the user when he makes a mistake.

But the point is, even if don't change anything I got block and error message appears. I can't see anymore where I got wrong on this code.

Anyone could help me?

IF (@error = 0) AND (@object_type in ('13')) AND (@transaction_type IN ('A'))
		BEGIN
			select @sTmp = 'TRUE',
				   @error_message = 
						case
							when ( T1.Price != T2.Price  ) then 'Price dismatch with base document! Please review the price!'
						end


			FROM [dbo].[OINV] T0 
				INNER JOIN [dbo].[INV1] T1 ON T0.[DocEntry] = T1.[DocEntry] 
				LEFT JOIN [dbo].[RDR1] T2 ON T2.[DocEntry] = T1.[BaseRef]
				INNER JOIN [dbo].[ORDR] T3 ON T3.[DocEntry] = T2.[DocEntry]
				where T3.[DocEntry]  = @list_of_cols_val_tab_del              
				and (
					 ( T1.Price != T2.Price )
					)


			if (@sTmp <> 'FALSE')
			begin
				set @error = 1
			end
		END