Why is it not allowing me to pay with my refund

Because the refund isn't yours yet. Should there be a problem with the refund or amount, or you get audited, the payment doesn't go through. They need payment from a different method.

 Why can’t I deduct the fees from my refund?
https://ttlc.intuit.com/community/charges-and-fees/help/why-can-t-i-deduct-my-turbotax-fees-from-my-refund/00/25621

Maybe your fees are higher than you think?   How to review your fees
https://ttlc.intuit.com/community/charges-and-fees/help/how-do-i-review-my-fees-in-turbotax-online/00/26353

For help with fees
https://ttlc.intuit.com/community/charges-and-fees/help/what-can-i-do-to-reduce-my-fees/00/26051

That’s not true because i pay with my refund every year

A lot of people pay the fees from their refund.  It's very common.