Code-Snippets-Functions/Execute a function on a child site/WooCommerce/set-free-orders-to-on-hold.txt

function change_free_order_status( $order_id ) {  
    if ( ! $order_id ) {return;}            
    $order = wc_get_order( $order_id );
    if($order->get_total() <= 0):
        $order->update_status( 'on-hold' ); // Change to what you need 
    endif;
}
add_action('woocommerce_thankyou','change_free_order_status');