If you pass a CallbackOptions instance with a non-null callback URI to an asynchronous Veriplace method, then when the result of the request is ready, Veriplace will send an HTTP POST message to that URI. There are two modes with different message formats:

• A summary callback contains only basic information about the result -- the unique identifier of the request, and whether it succeeded or failed -- as form-encoded content, i.e. a query string. You can use additional API methods such as GetLocationById(User, Int64, Token, LocationOptions) to get the details. This was the only format supported prior to version 1.6. See CreateSummaryCallback(String).
• An extended callback fully describes the result as an XML or JSON document, containing all the properties for LocationRequestStatus or InvitationStatus. If you use this mode, the callback URI must be secure (https:) since the result may contain protected information such as user location and mobile number; using an insecure callback URI with an extended callback will cause Veriplace to reject your request with a BadParameterException. See CreateExtendedCallback(String).

The APIs that support asynchronous requests also have methods for decoding the callback messages into result objects: GetCallbackResult(HttpRequest, HttpResponse) and GetCallbackResult(HttpRequest, HttpResponse). If you are not using the SDK to decode callbacks -- i.e. if the callback URI points to a service on some other platform -- you may wish to use additional options for controlling the message format: see CreateExtendedCallback(String, String) and CreateFormEncodedExtendedCallback(String, String, String).