Since a Google Site does not allow you to simply copy and paste in HTML code to insert one of our widgets or iframe into your site, adding your paper to a Google Site is not done with a regular Paper.li embed. Instead, you will need to add one of their "gadgets" to embed your paper.
Within Google Site editing menu,
1. Insert > ... More Gadgets
2. Search for "Include gadget (iframe)" and select gadget.
3. In the next overlay, in the URL to content field, enter the URL of the paper, using https and adjust any of the other settings (width, height, etc) according to your needs.
Example: if your paper URL is http:/paper.li/something, enter https://paper.li/something.
4. Click Ok, then Save.
For Pro Papers on a Custom Domain