Input Box prompts Message Box

Hi,

I am writing some (fairly basic) code where a user inputs a number to an input box which is then copied to a cell but I am trying to add a little extra functionality whereby if the value input results in an error i.e. the details related to that number are 'not found' (by a vlookup with an if in a different cell) then an message box is displayed with "Not Found". I've had a bash with little success but I think it's mainly because I don't know where to place the lines in my code.

Hope you can help.

Thanks

Sub New_Search()

    Dim strSearch As String
    
    strSearch = InputBox("Enter Agreement No.", "New Search")
      
    If strSearch <> "" Then Sheets("Sold Lookup").Range("E5").Value = strSearch
    If strSearch = "" Then Sheets("Sold Lookup").Range("E5").Value = ""
    
End Sub