How to convert VBA responseText to a user-defined tuple?

Question

When trying to convert responseText to a user-defined object, I get the error: Sub or Function not defined.

How do I convert a tuple sent by the server in responseText? Some previous posts suggested of casting using CType but VBA can't seem to find it and gives a compiler error.

Here's my code with the user-defined type that should be assigned the tuple in responseText. Thanks

Type DblStrTuple
    StrikePrice As Double
    Volatility As String
End Type

---

Function GetCorrectPutStrikeAndVolatility(ByVal StockTicker, ByVal StrikePrice, ByVal TargetDate) As DblStrTuple

    Dim XmlHttp As Object
    Set XmlHttp = CreateObject("MSXML2.ServerXMLHTTP.6.0")
    Url = "http://192.168.1.9:5005/options/get_strike_price_and_volatiitlity?"

    FinalUrl = Url & StockTicker & "+" & StrikePrice & "+" & TargetDate

    XmlHttp.Open "GET", FinalUrl, False

    XmlHttp.send

    CorrectCallOptionStrikePrice = DblStrTuple(XmlHttp.responseText)

End Function