how can I access my servers with javascript via external IP

why can I only access my servers via my static external IP address using this URL “https://cors-anywhere.herokuapp.com”? Without this URL, CORS throws an error.

fetch(‘https://cors-anywhere.herokuapp.com/http://my external IP address’, { redirect: ‘follow’ }) .then(response => response.text()) .then(data => console.log(data)) .catch(error => console.error(‘Error:’, error));