The option to pay for TurboTax using your federal refund may not show available if your return contains IRS or state forms that have not been finalized yet. You’ll also need to have chosen the e-file option and you'll need to have a federal refund coming that is large enough to cover all fees. Otherwise, you'll need to pay with credit card.
You should be able to click on Review to the left, and it will show you a list of forms in your return that aren’t available yet. It should also show date they should become available.
Keep in mind, the IRS will not start accepting e-filed & returns until January 29, 2018.
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