How To Get Last Payment Made

I need to get the clientid, last payment date, and last payment amount. I have tried using MAX but this does not work. Can anyone see what I'm doing wrong? I get all payments and all dates. I'm summing the payment amount incase they made two payments on the same day, not likely but...

SELECT     dbo.tblLoan.Client_ID, MAX(dbo.tblPayments.PaymentDate) AS [Last Pay Date], SUM(dbo.tblPayments.AmountPaid) AS [Last Pay Amt]
FROM         dbo.tblLoan INNER JOIN
                      dbo.tblPayments ON dbo.tblLoan.Loan_ID = dbo.tblPayments.Loan_ID
GROUP BY dbo.tblLoan.Client_ID
HAVING      (dbo.tblLoan.Client_ID = @Client_ID)