Sidechain not visible or working (w/AAC in .m4a audio)?

On a new project, dragged three channels of audio (in this case, two of them are AAC codec in .m4a files) onto the timeline, went to the Fairlight page to set up ducking via the sidechain. Put "send" on track 1 and 3, and "listen" on track 2 with the compressor turned on.
When playing, I can see no sidechain signal in the graphic display, nor hear any ducking on track 2. I attach images below showing the configuration of 'send' on track 3, 'listen' on track 2, and no sidechain signal visible.
Suggestions?
When playing, I can see no sidechain signal in the graphic display, nor hear any ducking on track 2. I attach images below showing the configuration of 'send' on track 3, 'listen' on track 2, and no sidechain signal visible.
Suggestions?