Login to your Bigcommerce Admin.

From the left menu, go to Advance Settings -> Web Analytics

You should see a page similar to this:

Select Site Verification Tags

Click Save from the bottom right corner.

If you have previously used tags you might have the option already selected and tabs visible like so:

Click on the Site Verification Tags tab

In the text field for Site Verification Header Scripts enter the value copied from the Omnivore settings page:

Click Save from the bottom right corner.

Optional: How to check if the verification code is present on your website

go to your Bigcommerce store home page and verify that the site verification tag is indeed added to the html source. To do this go to website and check the source code of your BigCommerce Store frontend.

On the homepage of your website right click -> view page source and search for “google-site-verification” If the verification code has been added successfully, you will see code similar to this: 

Verify your website in Omnivore

Return to Omnivore and hit the Check Now button in Step 4 from the Set up now link on the Dashboard