Before Update Condition

[MKuria]

I have created a form for users to enter data in the following fields . I
would like to add the following condition
Rule – If > [Initial Move Scheduled Pickup Date] > [Service Start Date] And
< [Service Completion Date] then user must enter data in [service Notes]

I am new to this and not sure if I should add the condition under scheduled
pickup date or service notes.
This is what I have under Service notes and it is not working -
Private Sub Service_Notes_BeforeUpdate(Cancel As Integer)
If (Me. Initial Move Scheduled Pickup Date >Me.Service Start Date And
<Me.Service Completion Date) Then
MsgBox "Date Entered is not within Service dates - Explain ",
vbCritical
Cancel = True
End If
End Sub