What form do I send in with my payment of due taxes. Where is that voucher?

You will send Form 1040-V with you payment. Please see these printing instructions if the 1040-V didn't print before:

1. In TurboTax Online, sign into your account.
2. Select Tax Home in the left menu.
3. Scroll down to Your tax returns & documents.
4. Select Add a State (you're not actually adding a state, this opens the return back up)
5. Select Tax Tools on the left and then Print Center and choose the print center

Please see IRS Paying Your Taxes for other payment options.

If you go to the "print" menu and print the return you will see everything including the voucher