Blocked script when using the REST API?

Why am I getting a blocked script when using the REST API?

Access to XMLHttpRequest at '[https://developer.shotgunsoftware.com/rest-api//api/v1/auth/access_token%7D](https://www.google.com/url?q=https://developer.shotgunsoftware.com/rest-api//api/v1/auth/access_token%257D&sa=D&source=hangouts&ust=1606935912330000&usg=AFQjCNFNJZUJJarwsgGZC07Ea02Pxokg3A)' from origin '[http://localhost:8080](https://www.google.com/url?q=http://localhost:8080&sa=D&source=hangouts&ust=1606935912330000&usg=AFQjCNHOR7uyXDM36DZ5FqSZ2fMHUzJFjA)' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I also tried from jsfilddle and got the same error

Access to XMLHttpRequest at 'https://studiodashboard.shotgunstudio.com/api/v1/entity/tags/_search' from origin 'https://fiddle.jshell.net' 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.