public async Task CreateAsync(Guid settlementId, Guid userId, string name, decimal cost)
{
var settlement = await _settlementRepository.GetSettlementOrFailAsync(settlementId);
var expense = new Expense(Guid.NewGuid(), userId, name, cost);
await _settlementRepository.AddExpenseAsync(expense, settlementId);
var user = await _userRepository.GetAsync(userId);
user.AddSettlement(settlementId);
manager.Settle(settlement);
}