Reason: CORS request did not succeed

The HTTP request which makes use of CORS failed because the HTTP connection failed at either the network or protocol level. The error is not directly related to CORS, but is a fundamental network error of some kind.

In many cases, it is caused by a browser plugin (e.g. an ad blocker or privacy protector) blocking the request.

Other possible causes include:

• Trying to access an https resource that has an invalid certificate will cause this error.
• Trying to access an http resource from a page with an https origin will also cause this error.
• As of Firefox 68, https pages are not permitted to access http://localhost, although this may be changed by Bug 1488740.
• The server did not respond to the actual request (even if it responded to the Preflight request). One scenario might be an HTTP service being developed that panicked without returning any data.

• CORS errors
• Glossary: CORS
• CORS introduction