I just installed a decora smart dimmer to control 4 lights in an atrium. The lights are part of a 3-way switch where one side is a simple switch and the side I rewired was a dimmer. I can get the dimmer switch installed to the point that the locator LED will turn on and the LEDs representing the dimmer work, but the lights they are supposed to control will no longer turn on from either side. The weird thing about my setup is that neither switch has 14-3 wiring to them, only 14-2. I’m not sure if I’m just out of luck on being able to put in a smart switch, or if there might be a simpler fix that I’m missing.
Note that the red wire was just the only color of extra wire I had laying around to connect the neutral wires to the switch.