Y can’t I pay with My federal refund

You will not be able to pay with your refund until all forms are finalized. 

The IRS will not be accepting returns until January 29 at the earliest. In order to pay with your refund, you will need to sign into your account and select the option after all of the forms have been finalized. 

And then your refund has to be big enough to cover all the fees plus the EXTRA 39.99 Refund Processing Service charge.  You should try to pay first with a credit card or prepaid card to avoid that extra charge.