Iterating over rows in table and portioning totals by group

Hey,

I've used a function to solve this. 
The function creates to total received and running total for due.
It then wil create a new column for receiverd.
Based on a index it wil then check if de record is the last record of the particular plan. if so it wil calculate the remainder.

Please try this code:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCshJzDPUDaksSDVU0lEyNDCAkwZKsTrI8kZAMSOwjAVOeWOoDHZZE7gsyAaYvBGa7UZopqPLY5M1gstaQIyAyxuj6TZBMx1dHpesKT5JhFZdoLrYWAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Plans = _t, Due = _t, Received = _t, #"Difference (wanted)" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Plans", type text}, {"Due", Int64.Type}, {"Received", Int64.Type}, {"Difference (wanted)", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Plans"}, {{"Table", each _, type table [Plans=nullable text, Due=nullable number, Received=nullable number, #"Difference (wanted)"=nullable number]}}),
    
    // function
    fnRunningtotal = (vTable as table) =>
    let
        add_index = Table.AddIndexColumn(vTable, "Index", 1, 1, Int64.Type),
        add_DueTotal = Table.AddColumn(add_index, "DueTotal", each List.Sum(List.Range(add_index[Due], 0, [Index]))),
        add_ReceivedTotal = Table.AddColumn(add_DueTotal, "ReceivedTotal", each List.Sum(add_DueTotal[Received])),
        add_Received = Table.AddColumn(add_ReceivedTotal, "ReceivedNew", each if [Index] = List.Max(add_ReceivedTotal[Index]) then  [Due] + ([ReceivedTotal] - [DueTotal]) else if [ReceivedTotal] >= [DueTotal] then [Due] else [DueTotal] - [ReceivedTotal], Int64.Type),
        add_Difference = Table.AddColumn(add_Received, "Difference", each if [Index] = List.Max(add_Received[Index]) then [DueTotal] - [ReceivedTotal] else 0, Int64.Type) 
    in
        add_Difference,

    inv_fnRunningtotal = Table.TransformColumns(#"Grouped Rows", {"Table", fnRunningtotal}),
    #"Expanded Table" = Table.ExpandTableColumn(inv_fnRunningtotal, "Table", {"Plans", "Due", "ReceivedNew", "Difference"}, {"Plans.1", "Due", "Received", "Difference"})

in
    #"Expanded Table"