Check if Value Exists in Another Sheet

[jazz2409]

Hello, how do I change the below code so when I enter a value on column M via paste it will return a messagebox saying "invalid data"?
the below code works however it isn't limited to just column M. it happens to all cells

Private Sub Worksheet_Change(ByVal Target As Range)

Dim FindString As String
Dim Rng As Range
On Error Resume Next


FindString = Range("M2").Value


If Trim(FindString) <> "" Then
    With Sheets("IDs").Range("A:A") 'searches all of column A
        Set Rng = .Find(What:=FindString, _
                        After:=.Cells(.Cells.Count), _
                        LookIn:=xlValues, _
                        LookAt:=xlWhole, _
                        SearchOrder:=xlByRows, _
                        SearchDirection:=xlNext, _
                        MatchCase:=False)
        If Not Rng Is Nothing Then
            
        Else
            MsgBox "Invalid Data!" 'value not found
            Target.Clear
            
        End If
    End With
End If
    
End Sub

Please help thank you