SOLID [L] - Wrong Method

solid-L-wrong-method.cs

public abstract class Transaction
{
    public long OriginalAmount { get; set; }
}

public class CreditCardTransaction : Transaction
{
    public long InterestAmount { get; set; }
}

public class PixTransaction : Transaction
{
}

// class that needs transaction 
public class Order
{
    // ctor and some properties

    public long TotalPaid { get; private set; }

    // wrong method
    public void AddTransaction(Transaction transaction)
    {
        var totalPaid = transaction.OriginalAmount;

        if (transaction is CreditCardTransaction)
        {
            totalPaid += ((CreditCardTransaction)transaction).InterestAmount;
        }

        this.TotalPaid += totalPaid;

        // do something more
    }
}