This is a macro developed earlier by Graham Mayor for which I'm very grateful and which works superbly well up to a point identified below - but only because I've "messed around" with it to try and achieve a solution.

Here is the macro:
Sub ReplaceFieldsV4()
    'Graham Mayor - http://www.gmayor.com - Last updated - 24 Sep 2018
    '===================================
    'this procedure ensures that all the Standard Numbering SEQ fields have the \s option set
    'irrespective of what had been put there earlier.
    Dim oFld As Field, oNewFld As Field
    Dim oRng As Range, oSeq As Range
    Dim figRng As Range, figLvl As Long
    
    ActiveWindow.View.ShowFieldCodes = True
    For Each oFld In ActiveDocument.Fields
        If oFld.Type = wdFieldSequence Then
            If InStr(1, oFld.Code, "Figure") > 0 Then
                oFld.Select
                'this procedure inserts a Chapter Figure caption based on Word Headings levels
                With Selection
                    Set figRng = .Range
                    Set figRng = figRng.GoTo(What:=wdGoToBookmark, Name:="\HeadingLevel")
                    figLvl = Right(figRng.Paragraphs.First.Style, 1)
                End With
                oFld.Code.Text = Replace(oFld.Code.Text, oFld.Code.Text, "SEQ Figure \* ARABIC \s \* MERGEFORMAT")
                oFld.Update
                Set oRng = oFld.Code
                With Selection
                .MoveLeft Unit:=wdCharacter, Count:=1
                .TypeText Text:="-"
                .Collapse
                .MoveLeft Unit:=wdCharacter, Count:=1
                End With
                'now adds the StyleRef field
                Set oNewFld = ActiveDocument.Fields.Add(Range:=.Range, _
                    Type:=wdFieldEmpty, _
                    Text:="StyleRef ""Heading " & figLvl & """ \s", _
                    PreserveFormatting:=False)
                oNewFld.Update
                Set oRng = oNewFld
            End If
        End If
    Next oFld
    ActiveWindow.View.ShowFieldCodes = False
lbl_Exit:
    Set oFld = Nothing
    Set oNewFld = Nothing
    Set oRng = Nothing
    Exit Sub
End Sub
What should happen is that a StyRef field should be inserted before the SEQ field, however, and error kicks in at this position here (in red):

                Set oNewFld = ActiveDocument.Fields.Add(Range:=.Range, _
                    Type:=wdFieldEmpty, _
                    Text:="StyleRef ""Heading " & figLvl & """ \s", _
                    PreserveFormatting:=False)
                oNewFld.Update
                Set oRng = oNewFld
...and this is the error message which appears:

Capture.PNG

I've tried "fiddling" with possible permutations to get the field added but don't seem to have the correct procedure to get it right.

Could the correct code be pointed out me, please, to achieve the process?

Thanks

Roderick