1. Go to the Website Visitors Tab, then "Setup". The first step is to click the "Add New" button.

2. Enter your domain. Click "Get the Pixel"
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3. Log in to your Wix account. From the domain dashboard, click "Settings".
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4. Click "Custom Code" in the "Advanced" section.

5. Add a custom code - paste the script from Instantly to the Header.
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6. Go back to Instantly and test the script.
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If the test is successful, you can close the window. Now you can proceed to create a Slack notification or a filtered view for your site visitors.
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Here's the video explaining the steps:
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