In that case the appointment item content does not match your description of that content. The code was specific to what you said.
The best I can suggest without access to the item is to offer a macro that will bar code the selected text in the appointment body. Select the number you want coding and run the following.
Code:
Sub BarCodeSelected()
'Graham Mayor - https://www.gmayor.com - Last updated - 06 Apr 2021
Dim olItem As AppointmentItem
Dim olInsp As Outlook.Inspector
Dim wdDoc As Object
Dim oRng As Object
Dim oPara As Object
Dim i As Integer
Dim sNum As String
Set olItem = Application.ActiveExplorer.Selection.Item(1)
With olItem
.Save
Set olInsp = .GetInspector
Set wdDoc = olInsp.WordEditor
Set oRng = wdDoc.Windows(1).Selection.Range
sNum = oRng.Text
oRng.Fields.Add oRng, 99, Chr(34) & sNum & Chr(34) & Chr(32) & "CODE39" & " \t", False
End With
lbl_Exit:
Exit Sub
End Sub