I am not going to provide pictures because I think i can explain it better. If pictures are needed I can post them.

I have a hallway light that is controlled by 2 switches.

I wanted to be able to control it with home assistant so I installed one HS210. It never worked properly so i took it apart to fix and I have tried so many different combinations of wiring based on everything I read and i can't get it to work they way I thought it would.

Expectation.

Turn on or off the light with the HS210 (from the switch itself or the app)

Turn on or off the light with the pre-existing dumb switch.

I have almost achieved this. The only issue was when i switched the pre-existing dumb switch the smart switch wouldn't turn it back on (however the smart switch DID NOT lose power)

Here is the wiring setup.

HS210 junction box

2 wire (white, black) coming from panel

3 wire (white, black, red) going to dumb switch

2 wire (white, black) going to light fixture

The dumb switch is the original 3 way switch with a common and 2 traveler poles

I even bought another HS210 thinking I could replace the dumb switch with it but I can't make that work either.

Please help me fix this based on my expectation or maybe it can't work this way?