After you file

It should offer you that option to pay the product fees out of the Federal refund, unless you encounter one of the following:

Is your Federal refund large enough to pay the product fees, sales taxes (if any), AND the additional 39.99 service fee for that option (44.99 for California filers)?

Also, all your Federal forms that you need must be available for efiling.  If you have some that are not yet ready, you won't have that payment option.  You can check here:
https://ttlc.intuit.com/questions/1908854-irs-forms-availability-table-for-turbotax-individual-perso...

Also, in order to get that "pay out of refund" option, you must meet these additional requirements:

    You must select to efile the return.   
    You must choose direct deposit for the refund.  You cannot choose a check in the mail.
    You must have a USA address.
    You must not split the deposit on Form 8888, as you mentioned above.

You will avoid the 39.99 (or 44.99) service fee if you don't choose that option, and instead pay upfront with credit/debit card or a prepaid debit card you can buy in a store.

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