Do I have to do anything beyond paying what I owe if I already paid through turbotax? I got a letter from the IRS stating I owe them the exact amount I paid via Turbotax.

TT pays nothing ... you entered the debit information and that is sent to the IRS with the return and once the return has been accepted they IRS is  responsible for completing  the payment transaction.  So did you see the payment being made from the account you indicated it should be done?  That is the only proof you have that the payment was made.   

Review the notice carefully ... does it say the debit was rejected ?   Review what info you entered into the program ... is it correct ?  

How did you pay though Turbo Tax?  Your only proof of payment is your bank statement or credit card showing the payment coming out. Turbo Tax only passes your bank account number to the IRS or state for them to take it out of your account.

If you selected "I will pay by bank debit", check with your bank account to make sure the money was actually withdrawn.  If yes, send proof to the IRS.  If no, you might have put a typo in the account number or the bank rejected the debit for some reason, and you owe the payment.

If you selected "I will pay by credit card" you were taken to a credit card company web site to put in your information.  Check your credit card account.  If no payment was made, you might have put a typo in the account number or the bank rejected the debit for some reason, and you owe the payment. If the payment was made, send proof to the IRS.

If you selected "I will pay on my own" then you need to make a payment.  You can mail a check or make an electronic payment on the IRS web site at www.irs.gov/payments.