// Javascript "CallServer" funtion
public void RaiseCallbackEvent(String eventArgument)
{
// Set amount and email
JSONObject json = JSONObject.CreateFromString(eventArgument);
Int16 amount = Convert.ToInt16(json.Dictionary["amount"].ToString());
string email = json.Dictionary["email"].ToString();
// Create checkout preference
Preference preference = CreatePreference(amount, email);
// Return checkout init point
returnValue = preference.InitPoint;
}