Will be returned? Or thats what you are getting?
Sounds like you are not using the correct opaqueID
You need to obtain the window.Twitch.ext.viewer.opaqueId from the frontend of the user that you wish to message.
And opaqueID (Required Technical Background | Twitch Developers) is not the users real Twitch ID, but their “extension user session ID” so it starts with a ‘A’ or a ‘U’ (Extensions | Twitch Developers)
So 204, means everything worked on Twitch’s side, which suggests to me that the opaque ID you are sending to is not correct.
So when you listen here
window.Twitch.ext.listen(‘whisper-’ + window.Twitch.ext.viewer.opaqueId
You need to use the same ID when sending.
This shouldn’t make a difference.
But make sure the extension is installed and active on the channel you are using in the view (just to be on the same side)
And make sure the view has the right channelID applied to it.
You can get the opaque ID from the view itself.