How to insert collection in VBA/Json

I need to insert a collection called Tax Class within Json format/Ms access VBA code which is now almost complete see current results below:

Current results

{
   "PosSerialNumber": "102010",
   "IssueTime": "2019-09-15",
   "Customer": 1,
   "TransactionTyp": 0,
   "PaymentMode": 0,
   "SaleType": 0,
   "Items": [
      {
         "ItemID": 1,
         "Description": "Apple (Rgb 350 ML)",
         "BarCode": "6009803227328",
         "Quantity": 15,
         "UnitPrice": 41,
         "Discount": 0,
         "Taxable": [
            {
               "Total": 615,
               "IsTaxInclusive": "True",
               "RRP": 52.8
            }
         ]
      },

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Expected results

{
   "PosSerialNumber": "102010",
   "IssueTime": "2019-09-15",
   "Customer": 1,
   "TransactionTyp": 0,
   "PaymentMode": 0,
   "SaleType": 0,
   "Items": [
      {
         "ItemID": 1,
         "Description": "Apple (Rgb 350 ML)",
         "BarCode": "6009803227328",
         "Quantity": 15,
         "UnitPrice": 41,
         "Discount": 0,
         "Taxable": [
              "B"
               ]
            {
               "Total": 615,
               "IsTaxInclusive": "True",
               "RRP": 52.8
            }
         ]
      },

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Amendment required on VBA

How do I include the new collection ("tax category") in the below VBA to hold ["B"] just below "taxable"

Private Sub CmdSales_Click()
  
'  Const SQL_SELECT As String = "SELECT * FROM Qry3;"
    
  Dim db As DAO.Database
  Dim rs As DAO.Recordset
  Dim fld As DAO.Field
  Dim qdf As DAO.QueryDef
  Dim prm As DAO.Parameter
  Dim root As Dictionary
    Set root = New Dictionary

    Dim transaction As Dictionary
    Dim transactions As Collection
    Dim item As Dictionary
    Dim items As Collection
    Dim invoice As Dictionary
    Dim invoices As Collection

    Dim i As Long
    Dim j As Long
    Set transactions = New Collection
  Set db = CurrentDb
  Set qdf = db.QueryDefs("Qry4")
For Each prm In qdf.Parameters
    prm = Eval(prm.Name)
Next prm
Set rs = qdf.OpenRecordset()

Set qdf = Nothing
 rs.MoveFirst
    Do While Not rs.EOF
        Set transaction = New Dictionary
        transaction.Add "PosSerialNumber", DLookup("PosSerialNumber", "tblInvoice", "Inv =" & Me.CboInv)
        transaction.Add "IssueTime", DLookup("IssueTime", "tblInvoice", "Inv =" & Me.CboInv)
        transaction.Add "Customer", DLookup("Customer", "tblInvoice", "Inv =" & Me.CboInv)
        transaction.Add "TransactionTyp", 0
        transaction.Add "PaymentMode", 0
        transaction.Add "SaleType", 0

        '--- loop over all the items
        Dim itemCount As Long
        itemCount = 3
        Set items = New Collection
        For i = 1 To itemCount
            Set item = New Dictionary
            item.Add "ItemID", i
            item.Add "Description", DLookup("Description", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))
            item.Add "BarCode", DLookup("BarCode", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))
            item.Add "Quantity", DLookup("Qty", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))
            item.Add "UnitPrice", DLookup("unitPrice", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))
            item.Add "Discount", DLookup("Discount", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))

            '--- loop over all the invoices
            Dim invoiceCount As Long
            invoiceCount = 1
            Set invoices = New Collection
            For j = 1 To invoiceCount
                Set invoice = New Dictionary
                invoice.Add "Total", DLookup("TotalAmount", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))
                invoice.Add "IsTaxInclusive", DLookup("Inclusive", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))
                invoice.Add "RRP", DLookup("RRP", "Qry4", "Inv =" & Me.CboInv & " AND ItemesID =" & CStr(i))
                invoices.Add invoice
            Next j
            item.Add "Taxable", invoices
            items.Add item
        Next i
        transaction.Add "Items", items
        
        rs.MoveNext
    Loop
    
    root.Add "", transaction

    Dim json As String
    json = JsonConverter.ConvertToJson(transaction, Whitespace:=3)
    Debug.Print json

End Sub

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Frankly I'm struggling on this topic because it appears there is not enough reading material out , I have checked around there is NOT even a book covering Json/VBA , may this could be a new subject.