I’m not sure what additional information I can provide because there isn’t that much.
A Snoop channel whispers audio into the channel it is snooping on, no matter where that channel is. It does this transparently to that channel.
A Snoop channel is a normal channel and can be bridged to other things, or playback called on it, or if spying then record.
You have to connect it to SOMETHING that is providing the audio to inject.
Creating a Snoop channel and connecting it to nothing won’t do anything.
Keeping the supervisor channel in the same bridge as the agent and caller won’t work if you want to whisper to a single channel. It just won’t. Trying that will just result in it failing every time when you unmute them.