How to attach a file to an order email in Opencart?

Question

opencart

Opencart does not allow you to attach a file in the checkout by default (for example, a client wants to attach his details or a print to the order). But at the same time, it has custom fields, with which you can display the field for attaching a file in the checkout on the site.
This is exactly what I used. Everything works, only the file is uploaded to the hosting upload and that's it, but, in theory, it should be attached as an attachment to the order letter to the site administrator.

Question: how to make sure that this same file comes as an attachment in a letter? Has anyone encountered this?

Answer 1

the mail library has a method
public function addAttachment($filename) {