Muss die skalare Variable - dapper mit asp.net-Kern deklarieren

Dies ist meine erste adrette Erfahrung. Ich habe hier Vorschläge gelesen, aber keiner scheint mein Problem zu beheben.

Must declare the scalar variable "@tranAmount".

Einige schlugen vor, wenn die fragliche Variable null ist. aber ich habe überprüft, es ist nicht null.

Ich hoffe, jemand könnte darauf hinweisen, was ich falsch mache.

public void RunEndOfDays()
        {
            try
            {
                IEnumerable<Loan> loans = null;
                var currentMonth = DateTime.Now.Month; //current month
                var currentYear = DateTime.Now.Year;

                using (var conn = new SqlConnection(ConnectionString))
                {
                    conn.Open();

                    loans = conn.Query<Loan>("Select * from Loan");

                    foreach (var loan in loans)
                    {
                        //now calculate the interest for this item
                        var interestInPercentage = loan.InterestRate / 100;
                        var interestPerDay = interestInPercentage / 365; //saved
                        var interestAmountPerDay = loan.AmountWrittenOff * interestPerDay;
                        var tranAmount = loan.AmountWrittenOff + interestAmountPerDay;//saved
                        var tranDate = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.FFF");
                        var loanAccountNo = loan.LoanAccountNo;
                        var originalLoanAmount = loan.OriginalLoanAmount;
                        var narration = loan.WrittenOffReason;


                        var addDailyInterest = @"INSERT INTO DailyInterest(LoanAccountNo,
                                                                        TranAmount,
                                                                        InterestRatePerDay,
                                                                        interestPerDay,
                                                                        AmountPerDay,
                                                                        OriginalLoanAmount,
                                                                        Narration,
                                                                        TranDate) VALUES(@loanAccountNo,
                                                                                         @tranAmount,
                                                                                         @interestInPercentage
                                                                                         @interestPerDay,
                                                                                         @interestAmountPerDay,
                                                                                         @originalLoanAmount,
                                                                                         @narration,
                                                                                         @tranDate)";
                        //conn.Open();
                        conn.Execute(addDailyInterest, loans);

                    }

                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error: " + ex.ToString());

            }

        }

Vielen Dank