Auto Complete Paid Orders if all products are virtual

functions.php

<?php 
// Place this in theme or your own agency plugin
 
add_filter( 'woocommerce_payment_complete_order_status', 'complete_paid_orders', 10, 2 );

/**
 * Auto Complete Paid orders in WooCommerce 
 * only if all products are virtual in the order 
 *
 * @author Jamie Madden <[email protected]>
 * @return string order_status
 */
function complete_paid_orders( $order_status, $order_id ) {
	
	$order = new WC_Order( $order_id );
	$order_items = $order->get_items(); 

	$virtual = false; 

	foreach ( $order_items as $item ) {
		$product = new WC_Product( $item[ 'product_id' ] ); 
		$virtual = ( $product->is_virtual() ) ? true : false; 
	}

	if ( $virtual ) { 

		if ( $order_status == 'processing' && ( $order->status == 'on-hold' || $order->status == 'pending' || $order->status == 'failed' ) ) {
			return 'completed';
		}

	}

	return $order_status;

} // complete_paid_orders()

?>