Function to conect to Firebase Rest API via Access VBA

This is the application for small school, which will store students' info in Firebase and also retrieve data from Firebase. I am using JSON Parser to parse the data and save the same in Access tables.

I am using this function in MS Access to connect to the Firebase. Please tell me if I am doing anything in an inefficient manner.

Function:

'---------------------
'#### FUcntion to make all web request and get data ####
Public Function ApiFirebaseCall(ByVal apiURL As String, _
                                ByVal Method As String, _
                                Optional ByVal apiBody As String) As String
'On Error GoTo Sub_Err

    Dim reader As New XMLHTTP60

    Debug.Print Method & " = " & apiURL
    Debug.Print "BODY" & Nz(apiBody)

    'Open URL of API
    reader.Open Method, apiURL

    If IsNull(apiBody) Or apiBody = "" Then
    'In case of GET
        reader.send
    Else
    'In case of POST, PATCH, DELETE
        reader.send (apiBody)
    End If

    'Using since is was mentioned in SO. Don't know the reason why
    Do Until reader.ReadyState = 4
        DoEvents
    Loop

    If reader.Status = 200 Then
    'The API was sucessful
        If reader.responseText <> "null" Then
        'Now check if the response contains data
            ApiFirebaseCall = reader.responseText
        Else
            MsgBox reader.responseText
            ApiFirebaseCall = "Error"
        End If
    Else
    'The API Call was not sucessful
        MsgBox reader.responseText
        ApiFirebaseCall = "Error"
    End If

    'Debug.Print "Reader Response - " & reader.responseText

'Error Catching
Sub_Exit:
    Exit Function
Sub_Err:
    ApiFirebaseCall = "Error"
    MsgBox Error$
    Resume Sub_Exit

End Function

Example function call:

Dim apiURL, response As String
apiURL = apiBaseURL & "/d.json?auth=" & apiAuthKey
response = ApiFirebaseCall(apiURL, "GET")

'Forward processing to next function, if API Call was sucessfull
If response <> "Error" Then
    JsonParser (response)
End If