I'm trying to get notifications set up via Outlook similar to a post I found here for Prowl: http://bubba.org/index.php?id=461091729996829223. It seems I can authenticate correctly, but I keep receiving errors of "Not allowed to send to user". I've tested the same string using a basic curl example as in the API docs. Am I missing something glaringly obvious?

Strings in "[]" are filled with the appropriate values, of course.

Public Sub NotifoBroadcast()
Dim usernames As Variant
Dim curUsername
Dim RequestString

usernames = Array("[SUBSCRIBED_USER1]", "[SUBSCRIBED_USER2]")

For Each curUsername In usernames
Set oHTTP = CreateObject("Microsoft.XMLHTTP")
user = "[SERVICE_USER]"
apikey = "[APIKEY]"
URL = "https://api.notifo.com/v1/send_notification"
RequestString = "to=" & curUsername & "&msg=Message"
oHTTP.Open "Post", URL, False
oHTTP.setRequestHeader "Authorization", "Basic " + "[BASE_64_ENCODED_CREDENTIALS]"
oHTTP.Send RequestString
Result = oHTTP.responseText
MsgBox Result
Set oHTTP = Nothing
Next curUsername
End Sub