How to get product_id of WooCommerce order in functions.php

Question

I am trying to create a IF condition with product_id by getting it from order_id, when a new order is placed.

I tried it like:

add_action('woocommerce_new_order', 'wc_send_order_to_mypage');
function wc_send_order_to_mypage($order_id)
{
    $order = wc_get_order( $order_id );

    foreach ($order->get_items() as $item_key => $item )
    {
        $product_id   = $item->get_product_id(); 

        if ( $product_id == 29 ) {
            $url = "https://www.abc.de";
        }

    }
    //do something with $url
}

But each time when I want to place the order, woocommerce is giving me the error message "Internal Server error".

I tried to use code from this answer but somehow it does not work: How to get WooCommerce order details

What is not working here? Thank you very much for your help.

Best regards,

Thomas