How to find the products associated with a WooCommerce subscription

get-product-from-subscription.php

/**
 * How to get the product associated with a WooCommerce subscription
 */
function ct_checkout_subscription_created( $subscription, $order, $recurring_cart ) {
	$id = $subscription->get_id(); // You can use this to set meta in the subscription
	// Get the products in the order
	$items = $order->get_items();
	foreach( $items as $item ) {
		$product = $item->get_product();
		$product_id = $product->get_id();
		// ... Do your stuff here
	}
}
// Use any hook that passes the $subscription object
add_action( 'woocommerce_checkout_subscription_created', 'ct_checkout_subscription_created', 10, 3 );