training access vba london - Word vba

am preparing a template and am asking a question which i need a message box to appear. i have inserted the following code

Private Sub EUVAT_Click()
If BillAmounts.EUVAT = Yes Then
Sub NewMessage()
MsgBox("Is the Client VAT number shown above correctly?", vbYesNo) = vbYes
End If
End Sub

when i click yes in the template BillAmounts gets highlighted and error Expected End Sub.

I would be grateful for some help, I havent done any vba since training in June !