How to show custom field after purchase in customer order details page in Woocommerce?

I want to show specific text in my custom field after customer completes the purchase of the product.

However something wrong with my code:

If I use this code without woocommerce_order_details_after_order_table, it will work on all order pages no matter the order status:

Could you please help? How to correctly insert code to order-details.php so the customer will be able to see custom field only after completing the purchase?