The enhanced E-commerce Tracking with gtag.js that will save your time. Modified from https://www.opencart.com/index.php?route=marketplace/extension/info&extension_id=26875

remarks:
- this tracking will only working with gtag.js
- must enable enhanced e-commerce tracking view in your Google Analytics
- tracking data only covers basic details (transaction id, amount, items, etc.)
- only tested in OC 3.0.2.0.

Just paste the xml file into your vqmod. that's it for installation.

* i make this extension available for free to contribute back to the open source community. if you appreciate my work https://paypal.me/sapienstech