How to execute an additional code upon successful payment of an order in Opencart?

Question

JavaScript

I'm trying to connect Modulkassa to Opecnart 2.2
I'm new to opencart code, so I need your help.
I use this library: https://github.com/bigperson/modulpos-php-api-client
I successfully connected it to the engine (located in the vendor folder and connected via composer).
The situation is such that I need to send a check to the Modulkassa server at the moment when the payment system confirmed the debiting of money from the card. The question is, in which file, class and method, do I need to add my code for sending a check?

Answer 1

I threw everything the same on codepen - codepen.io/anon/pen/VaNMgB
Everything works.

Answer 2

Add the novalidate attribute to the form to disable html5 validation

Answer 3

checkout/success here