I'm trying to use object variables with a workbook and worksheet. I get the "Error 438, Object doesn't support this property or method"

When I run the code below I get the "Error 438, Object doesn't support this property or method" at the line: WBA.WS1.Range("I7").Select

Sub Sandbox()

    Dim WBA As Workbook
    Set WBA = Workbooks.Open(Filename:="C:\Reports\Sandbox_data.xlsb")

    Dim WS1 As Worksheet
    Set WS1 = WBA.Sheets("Rpt_Group")

    WBA.WS1.Range("I7").Select

End Sub