add_filter( 'wcfm_form_custom_validation', function( $form_data, $screen ) {
    if( 'product_manage' == $screen ) {
        if(isset($_POST['status']) && ($_POST['status'] == 'draft')) {
            $product_status = 'draft';
        } else {
            if( apply_filters( 'wcfm_is_allow_publish_products', true ) ) {
                $product_status = 'publish';
            } else {
                $product_status = 'pending';
            }
        }

        if( 'publish' == $product_status ) {
            if( isset( $form_data['manage_stock'] ) && 'enable' == $form_data['manage_stock'] ) {
                if( isset( $form_data['stock_qty'] ) && $form_data['stock_qty'] <= 0 ) {
                    $form_data = [
                        'has_error' => true,
                        'message'   => __( 'Stock quantity can not be 0 or less', 'wc-frontend-manager' )
                    ];
                }
            }
        }
    }

    return $form_data;
}, 10, 2 );