Thank you @bildnereiclick for your response and clarification. By default, our Flexible Shipping plugin allows to use the negative values which apply only to the shipping cost. It means that the negative values configured in the shipping cost calculation rules will subtract the shipping cost until it equals 0 and won’t go further affecting the price of the products in the cart.
However, if you want the shipping cost negative values to be deducted from the cart subtotal as well, you can achieve it by using the flexible-shipping/shipping-method/allow-negative-costs filter.
Once you add the following code to the functions.php file of your currently used theme/child-theme or apply it via Code Snippets plugin or similar one:
add_filter( 'flexible-shipping/shipping-method/allow-negative-costs', '__return_true' );
the negative shipping cost values will affect the cart subtotal as well.
Kind regards,
Luke
