bitcoin.cs

var inputList = new List<UnspentCoin>();
var unspentResponse = await client.ListUnspentAsync();
var unspentList = unspentResponse.OrderByDescending( x => x.Amount).ToList();
var inputBtcSum = new Money(0, MoneyUnit.BTC);
foreach (var unspent in unspentList) {
    if( inputBtcSum >= totalPaymentAmountBtc) break;

    inputBtcSum += unspent.Amount;
    inputList.Add(unspent);
}