I’m using the “WooCommerce - Account - View order” template and unfortunately I can’t use the dynamic variables, for example to obtain the post_id.
When this data is obtained, the result returned belongs to the “Account” page and not to the order I am viewing.
Since you are still on the my-account page, the post_id outputs the post id of the my-account page.
Theoretically, you could use the {woo_order_id} (which corresponds to the post id of the order). However, the dynamic data tag (and other woo_order tags) within the custom woo order template does not work yet.
I have added this as an improvement task to our to-do list and will move this report accordingly, as it is not a bug.