CORS Error: 'Access-Control-Allow-Origin' Header Missing - localhost:8080 to localhost:8081

This error message indicates that the browser is blocking a cross-origin request made by a web application running on 'http://localhost:8080' to a server running on 'http://localhost:8081'. This is due to the CORS (Cross-Origin Resource Sharing) policy implemented by the server, which restricts access to resources from different origins by default.

To fix this issue, the server should include the 'Access-Control-Allow-Origin' header in its response to the preflight request. This header should contain the value of the origin that is allowed to access the resource. For example, if the web application running on 'http://localhost:8080' is allowed to access the server, the header should be set to 'Access-Control-Allow-Origin: http://localhost:8080'.

If you do not have access to the server, you can try using a proxy server or a browser extension that allows you to bypass CORS restrictions. However, this should only be used for testing purposes and not in production environments.