Before we start the setup, we will assume you already have a google merchant account, if not I invite to follow this : How to create a Merchant Center Account or directly visit merchants.google.com

Verify and claim your website URL :
In the Business Information Section

Then you will to verify your domain by adding a meta tag to your layout ( head block section).
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Once this done you just need to ask google merchant center to verify your domain.

When creating an account, you may be redirected to Google Merchant Center Next.

If you want to switch to the classic version you do the following steps:

1.Click on the "Help" button

2.Click on the "Use classic Merchant Center" button

3.Choose the reason (optional) and click on the "Next" button

4.In the next two screens choose one option that fits you the best

5.Select the checkbox and click on the "change now" button

Merchant Center can automatically create a Google API Console project and associated service account key for you. Your application will authenticate with this key when using the Content API for Shopping.

Now open content-api-key.json in a text editor and copy its content to your app store settings as well as your merchant ID.
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The setup is now finish you will just have now to configure your Tax & Shipping settings.  ✊
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Next Step: Setup your feeds in the Admin Area.  
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