If you're connecting to the RPC server from within a browser, RPC origins are usually in the form SCHEME://HOST[:PORT], where SCHEME is typically https or http, HOST is your domain or ip, and PORT is the port of the webserver from which the user will be connecting (omitted for ports 80 and 443). For example, https://discord.com would be used if the user were connecting from https://discord.com/some/page/url

If you're connecting to the RPC server from within a non-browser application (like a game), you just need to make sure that the origin is sent with the upgrade request when connecting to the WebSocket. For local testing, we recommend testing with an origin like https://localhost