Check if a coupon is applied to cart in WooCommerce

I need to find a way to check if a coupon is applied to WooCommerce checkout, if so I would like to do something. I have tried searching around for this and cannot find a solution.

Here is a slimmed down version of what I am trying:

add_action('woocommerce_before_cart_table', 'apply_product_on_coupon');
function apply_product_on_coupon( ) {
    global $woocommerce;
    $coupon_id = '12345';
        
        if( $woocommerce->cart->applied_coupons === $coupon_id ) {
        echo 'YAY it works';
    }
}

So is this not the right way to check if the coupon exists in cart? if( $woocommerce->cart->applied_coupons === $coupon_id )

From your example, something like this might work. This is untested, but should give you a step in the right direction:

add_action('woocommerce_applied_coupon', 'apply_product_on_coupon');
function apply_product_on_coupon( ) {
    global $woocommerce;
    $coupon_id = '12345';
    $free_product_id = 54321;

    if(in_array($coupon_id, $woocommerce->cart->get_applied_coupons())){
        $woocommerce->cart->add_to_cart($free_product_id, 1);
    }
}