deduct-coupon-percent-for-fixed-commission

add_filter('wcfmmp_order_item_commission', function( $item_commission, $vendor_id, $product_id, $variation_id, $item_price, $quantity, $commission_rule, $order_id ) {
    if( isset( $commission_rule['mode'] ) && $commission_rule['mode'] == 'fixed' ) {
        $order = wc_get_order($order_id);
        $items = $order->get_items( 'line_item' );
        $item_total = 0;
        $item_subtotal = 0;
        if( !empty( $items ) ) {
            foreach( $items as $item_id => $item ) {
                $line_item = new WC_Order_Item_Product( $item );
                $item_product_id = $line_item->get_product_id();
                $item_variation_id = $line_item->get_variation_id();
                if( $item_variation_id && $item_variation_id != $variation_id || $item_product_id != $product_id ) continue;
                $item_line_item = $line_item;
                $item_total = $item_line_item->get_total();
                $item_subtotal = $item_line_item->get_subtotal();
                if($item_total == $item_subtotal) {
                    return $item_commission; //if no coupon applied commission unchanged
                }
                break;
            }
        }
        if( apply_filters( 'wcfmmp_is_allow_commission_fixed_per_unit', true ) ) {
            $item_commission = (float) $commission_rule['fixed'] * $quantity;
        } else {
            $item_commission = (float) $commission_rule['fixed'];
        }
        $item_commission = ( $item_commission * $item_total ) / $item_subtotal;
        if( (float) $item_price < (float) $item_commission ) {
            $item_commission = $item_price;
        }
        $admin_fee_mode = apply_filters( 'wcfm_is_admin_fee_mode', false );
        if( $admin_fee_mode ) {
            $item_commission = (float) $item_price - (float) $item_commission;
        }
    }
    return $item_commission;
}, 10, 8);