//Minha classe de callback
TTesteCallback = class(TDBXCallback)
public
  function Execute(const Arg: TJSONValue): TJSONValue; override;
end;

function TTesteCallback.Execute(const Arg: TJSONValue): TJSONValue;
begin
  // não faço nada, apenas para teste
  Result := TJSONTrue.Create;
end;

// código do botão de teste
var
  xCallBack,
  xSession : string;
begin

  if SQLConnection1.Connected then SQLConnection1.Close;
  SQLConnection1.Open;

  FCallbackManager := TDSClientCallbackChannelManager.Create(Self);
  FCallbackManager.DSHostname := 'localhost';
  FCallbackManager.DSPort := '211';
  FCallbackManager.UserName := '';
  FCallbackManager.Password := '';
  FCallbackManager.CommunicationProtocol := 'tcp/ip';

  xCallBack := TDSSessionHelper.GenerateSessionId;;
  xSession := TDSSessionHelper.GenerateSessionId;

  FCallBackClient := TTesteCallback.Create;

  {Guardando a Identificação do CallBack}
  FCallbackManager.CloseClientChannel;
  FCallbackManager.ManagerId := xSession;
  FCallbackManager.RegisterCallback(xCallBack,FCallBackClient);

  // FCallbackManager.UnregisterCallback(xCallBack);
  FCallbackManager.CloseClientChannel;

  // ao tentar executar a linha abaixo, da accessviolation
  FreeAndNil(FCallBackClient);
  FreeAndNil(FCallbackManager);

  Close;

end;