Ajax Request: Response to preflight request doesn’t pass access control check

Today, I started getting this error after making few Ajax calls to a remote server;

Access to XMLHttpRequest at 'https://foo.com' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

This problem relates to CORS. Here is some explanation and work around;

https://stackoverflow.com/questions/35588699/response-to-preflight-request-doesnt-pass-access-control-check

Here is some more useful info;

https://www.edureka.co/community/82342/how-to-add-custom-http-header-to-ajax-request-with-javascript