Apple TV 4K (2nd generation) won't learn TCL Volume control

I'm trying to make the ATV4K2 remote, control a TCL TV's volume/mute. (Mostly because of a horribly placed MUTE button which keeps triggering a setup screen when I hit it - trying to pause) (Good placement on ATV4K1 remote that should have never changed!)

The area to set this up is remotesanddevices/hometheatercontrol/volumecontrol

Select Volume Control - YES

Learn New Device - (Learn remote) hold volume up (on the TCL remote) etc.etc.

The error is - No signal detected ...blah blah blah.

It simply doesn't"see" the signal from the TCL TV's remote in order to learn it.

The ATV4K2 remote works fine.

The TCL TV remote works fine

I've even reset the ATV4K2 remote - no help.

All other settings on the ATV4K2 are default.

Any other ideas other than two fisted button pushing forever? :-)