get https://api.similarweb.com/v1/website/{domain.com}/unique-visitors/desktop_unique_visitors
Returns the daily or monthly unique visitors to a domain on desktop devices.
Price: 1 hit per request
Historical data goes back 37 months, depending on your subscription.
To retrieve 'Last 28 days', remove the start_date & end_date parameters from the URL and set granularity to daily.