It seems that you experienced a problem when item_Weight is only specified in one row of a group. Then try this long sequence too:
drop table if exists #tbl_Receivable, #tbl_Customer
Create table #tbl_Receivable (Rec_ID int,Inv_ID int ,Customer_ID int,Rec_Date date,Rec_Amount varchar(50),Inv_type varchar(50),item_Weight int);
Create table #tbl_Customer ( Customer_ID int ,Customer_Name varchar(50));
insert into #tbl_Customer values (1,'Akhter'), (2,'Hussian');
INSERT INTO #tbl_Receivable VALUES
(111,211,1,'2020-03-06',5000,'Payable',0),
(112,211,1,'2020-03-07',2000,'Received',0),
(113,222,1,'2020-03-08',8000,'Payable',0),
(114,223,2,'2020-03-08',2000,'Payable',0),
(115,222,1,'2020-03-09',4000,'Received',0),
(116,224,1,'2020-03-10',15000,'Payable',500),
(117,211,1,'2020-03-12',1000,'Received',0),
(118,224,1,'2020-03-11',15000,'Payable',0)
---
;
with E1 as
(
select
r.*,
cast(Rec_Amount as int) as amount
from #tbl_Receivable r
inner join #tbl_Customer c on c.Customer_ID = r.Customer_ID
),
E2 as
(
select
Inv_ID,
max(item_Weight) as item_Weight,
Customer_ID,
min(Rec_Date) as Rec_Date,
isnull(sum(case Inv_type when 'Payable' then amount end), 0) as Payable,
isnull(sum(case Inv_type when 'Received' then amount end), 0) as Received
from E1
group by Inv_ID, Customer_ID
),
E3 as
(
select
Inv_ID as Inv_ID0,
cast(Inv_ID as varchar(10)) as Inv_ID,
cast(item_Weight as varchar(10)) as item_Weight,
cast(Customer_ID as varchar(10)) as Customer_ID,
cast(Rec_Date as varchar(20)) as Rec_Date,
Payable,
Received,
Payable - Received as Pending
from E2
),
E4 as
(
select *
from E3
union all
select
2147483647,
'',
'',
'',
'TOTAL',
sum(Payable),
sum(Received),
sum(Pending)
from E3
)
select Inv_ID, item_Weight, Customer_ID, Rec_Date, Payable, Received, Pending
from E4
order by Inv_ID0
If still there are issues, then show the data to reproduce them, and the expected results.