You may be able to before long. It's likely your return does not yet qualify to efile since all your forms may not be finalized.
That payment option also requires efiling, direct deposit to receive the refund, and a USA address. And the Fed refund must be large enough to cover the product fees, sales taxes, and the 39.99 service fee for that payment method.
If you are in the FILE section and trying to file your 2017 return, and are trying to pay for it, if it's not offering you the option to pay out of the Federal refund, it's likely because at this point in early filing season some of your Federal forms are not finalized and available yet. When all your forms are available, it should let you see that option to pay out of refund, because the program must first be sure you will be able to efile.
Step through the REVIEW tab in the left
menu column to see what forms you are waiting for. Or look at the
tables I linked below.
Be aware that payment option has a 39.99 service fee, which you can avoid by paying upfront with credit card, debit card, or a prepaid debit card you can buy in a store for a few bucks.
Federal forms availability dates:
State forms availability dates:
The IRS will not start processing returns until January 29. If you efile before then, your return will just sit stockpiled on TurboTax servers until the IRS starts pulling them on January 29 (except for a few test returns pulled early.) You won't be able to retrieve the return if you notice a mistake, get an additional W-2, 1099, etc. If you efile at this early point in time and need to change something, you'd have to wait until after January 29 to first find out if your return was accepted or rejected. If rejected, you could make any change and resubmit. If accepted, that would require waiting on any refund, then preparing an amended return, which can be a hassle.
Also, if you have EIC (earned income credit, aka EITC) or ACTC (additional child tax credit), the IRS will start processing them on Jan. 29, but will not start releasing those refunds until February 15. That means people with those types of credits may not start receiving their refunds until around February 27.