SQL Server 2022

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8 rows affected

declare @ID int

select @ID = min(ID) from #ledger where Quantity > 0;

while @ID is not null
begin

with inbound as
(
  select ID, [Date], ProductID, Qty = Quantity
  from   #ledger
  where  ID = @ID
),
outbound as
(
  select l.ID, l.Date, l.ProductID, 
         Qty = -(l.Quantity + isnull(m.Match_Qty, 0)),
         CumQty = sum(-Quantity) over (partition by ProductID order by ID)
  from   #ledger l
         left join
         (
             select Outbound_ID, Match_Qty = sum(Match_Qty)
             from   #matches
             group by Outbound_ID
         ) m  on l.ID = m.Outbound_ID
  where  l.Quantity + isnull(m.Match_Qty, 0) < 0  
)
insert into #matches (Outbound_ID, Inbound_ID, Match_Qty)
select Outbound_ID = o.ID,
       Inbound_ID  = i.ID,
       Match_Qty   = m.Match_Qty
from   inbound i
       inner join outbound o on    i.ProductID = o.ProductID
                            and    i.[Date]   <= o.[Date]
       cross apply
       (
           select Match_Qty   = case when i.Qty >= o.CumQty
                                     then o.Qty
                                     when i.Qty >  o.CumQty - o.Qty
                                     then i.Qty - (o.CumQty - o.Qty)
                                     else 0
                                     end  
       ) m
where  m.Match_Qty > 0

select @ID = min(ID) from #ledger where Quantity > 0 and ID > @ID
  
end

select *
from   #matches

Outbound_ID	Inbound_ID	Match_Qty
2	1	2
3	1	3
4	1	2
5	1	1
7	1	2
7	6	1
8	6	2