public async Task <JsonResult> AddBalance(float sum)
        {
            try
            {
                await manageCustomer.AddBalanceAsync(User.Identity.Name, sum);

                return(Json(new {
                    ok = true,
                    error = string.Empty
                }));
            }
            catch (Exception exception)
            {
                return(Json(new {
                    ok = false,
                    error = exception.Message
                }));
            }
        }