using {id_order} in order_conf.html

[TurkeyFish]

PS 1.6

I'm trying to add the variable {id_order} to order confirmation emails. In the Payment Accepted email sent at the same time it works fine. The variable name is showing in the order confirmation email instead of the value.

I have tried following the instructions here

https://www.prestashop.com/forums/topic/372654-how-to-add-id_order-on-emailorder-conf/

The instructions are to add a line to the data array in override/classes/PaymentModule.php so that it reads:

$data = array(
                        '{firstname}' => $this->context->customer->firstname,
                        '{lastname}' => $this->context->customer->lastname,
                        '{email}' => $this->context->customer->email,
                        '{id_order}' => $order->id, 	

This doesn't work. I have forced recompile and cleared cache.

I had this working for a year, until recently a module screwed up my files and I had to reset everything and did not have backups. I took notes on changes, and my notes were that the above was the ONLY change I had to do, and yet it isn't working.