There is no bug ... there are restrictions.
In order to pay for your fees using your federal refund, you must have a refund high enough to pay the fees plus the EXTRA refund processing fee of $39.99 ($44.99 in CA). The amounts on line 28 for the child tax credit or line 30 for the recovery rebate credit do not "count" toward having a high enough refund. Is the amount on line 35a of your Form 1040 enough for the fees if you do not include those?
How can I see my TurboTax fees?
https://ttlc.intuit.com/questions/2565973-how-do-i-review-my-fees-in-turbotax-online
What is Refund Processing Service?
Or—-Use this IRS site for other ways to file for free. There are 8 free software versions available from the IRS Free File site if your AGI is $73K or less ...
https://apps.irs.gov/app/freeFile/
