We are on nopcommerce 3.7 and just curious if you guys can help me with this.

I am wanting to offer free shipping on orders over $99. I am able to do this and its working fine but we run into an issue when we have an item that is marked as an additional shipping charge. So for example if you add this item to your cart https://accessories.lazydays.com/LIP380400-380400-22733 it has a flat additional shipping charge of $150, so your order is now over $99 so you would qualify for free shipping on other items that are not marked as a flat rate with the truck symbol. So if you add this item to your cart now https://accessories.lazydays.com/dehco-rubber-roof-coating-white-13-1545-16-46128-4 it is nothing special not marked as free shipping or an additional shipping charge. But if you click estimate it will charge $150 for the couch and then $11 which is my calculated rate for orders $50-75. Why is it charging the $11? The order is over $99 so it should be free and the only shipping charge is the $150 for the couch?