public async Task CreatInvoice(NewBillDTO dto)
        {
            var user = await ServiceUnitOfWork.AccountRepository.FindAsync(dto.UserBill.Id);

            var trainings = new List <DAL.App.DTO.Training>();
            var bill      = new Bill()
            {
                AppUserId = dto.UserBill.Id,
                Deadline  = dto.Deadline,
                Total     = dto.Total,
            };

            bill = ServiceRepository.AddNewBill(bill);
            await ServiceUnitOfWork.SaveChangesAsync();

            foreach (var trainingdto in dto.Trainings)
            {
                var trainingInBill = new TrainingInBill()
                {
                    BillId     = bill.Id,
                    TrainingId = trainingdto.Id
                };
                await ServiceUnitOfWork.TrainingInBillRepository.AddNewTrainingInBill(trainingInBill);

                var training = await ServiceUnitOfWork.TrainingRepository.FindAsync(trainingdto.Id);

                trainings.Add(training);
            }


            await ServiceUnitOfWork.SaveChangesAsync();
        }