Problem with shipping cost when applying a discount

Good afternoon,

I have a problem applying a discount on the final price of a purchase. The question is: I want to apply a 20% discount on the purchase. In this store, once you exceed 30 euros, shipping is free, but if a user exceeds 30 euros and uses the discount, they lose the free shipping.

I would like to know if there is any possibility of solving this problem, that is to say, that in a purchase over 30€ in which the programmed discount is applied, the free shipping is not lost.

Thanks in advance.