First question: looking inside the javascript SDK file..
ValidateGooglePlayPurchase: function (request, callback) {
if (PlayFab._internalSettings.sessionTicket == null) throw "Must be logged in to call this method";
PlayFab._internalSettings.ExecuteRequest(PlayFab._internalSettings.GetServerUrl() + "/Client/ValidateGooglePlayPurchase", request, "X-Authorization", PlayFab._internalSettings.sessionTicket, callback);
},
should that be X-Authentication?