Printing over internet from iPad to cups

I would like to use my iPad Pro and print documents and files remotely over the internet to my office. Considering the iPad not being on the same network, I have installed and configured a Rasberry pi with Cups and it is working nicely while being on the same network.

I would like to know if there is any function that I can mix and match to achieve the goal. Since Google Cloud Printing is out of the game now, it is quite difficult to find an alternative.

Printing over internet from iPad to cups
 
 
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