Unable to send message outside Mathematica through Channel-Based Network

Question

Channel-Based communication is available since release 11.0 as an experimental functionality for publish-subscribe communication between WL sessions or with external systems.

Functionality works well between WL sessions, but when trying to send messages through external systems, I was unable to make this work.

myChannel = CreateChannel["demo", Permissions -> "Public"]
(*ChannelObject["https://channelbroker.wolframcloud.com/users/[email protected]/demo"]*)

listener = ChannelListen[myChannel];
Dynamic[listener["Message"]]

ChannelSend[myChannel, <|key -> "test"|>]
(*Message Successful*)

Prepare command for curl (or web browser)
url = URLBuild[listener["URL"], {"operation" -> "send", "Message" -> "yet another message"}]

(*"https://channelbroker.wolframcloud.com/users/user%40example.com/demo?operation=send&Message=another+message"*)

(*Sending Message through the Mathematica Session works*)
URLExecute[url]
(*message ID*)

When trying through terminal with curl URL, or through the web browser, the following message is displayed:

403 Forbidden

Answer 1

When copying a URL to external programs, make sure that you are using Edit > Copy As > Plain Text (Cmnd-Shift-C on Mac)... or otherwise remove the line continuation characters ("\") that the Front End inserts in the copied text.

As yet another trick, you can execute:

Hyperlink[url]

... and then click the output link. That will use the correct URL in your default web browser.