Here are the first steps that you need for publishing your listings on Google Shopping Free Listings :
Create your Google merchant account as described here
Click on Tools and settings icon on the top right corner
Fill all of the sections below Tools : Shipping and returns, Regions , Sales tax, Business Information
Make sure that your website is verified by Google (View image below)
Congrats! Your Google merchant account is now ready , let's start adding your store products into Google.
Go inside your WIX account -> on the left menu select our app named -> Google Shopping by shopUpz and upload your collection into Google shopping.
Here is a step by step Export listings from WIX to Google Shopping video tutorial
Below are Google merchant center settings menu and website verification approval
Make sure that your website is verified by Google merchnat center