Your Opencart requires a Google Analytics e-commerce tracking which don’t come default in your Opencart.
Base on the tips by http://www.notesonclick.com/blog/add-google-analytics-e-commerce-tracking-in-opencart/
We created a VQMOD version for developers easily have this function without extra coding.
You can download right here
https://www.opencart.com/index.php?route=marketplace/extension/info?extension_id=26875
It’s free!