Unable to retrieve notification token due to unsupplied origin

I'm running the Firebase Cloud Messaging example and caught up with this error:

> Failed to load https://fcm.googleapis.com/fcm/connect/subscribe: The 'Access-Control-Allow-Origin' header has a value 'https://localhost:8081' that is not equal to the supplied origin. Origin 'http://localhost:8081' is therefore not allowed access. Have the server send the header with a valid value, or, if an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Has anyone encountered the same issue and figured out how to solve it? Many thanks.