I am update one of the my 3 gang switch into 1 smart switch and 2 existing one.

the existing switch have standard 3 wire. 2 hot and 1 ground as photo below. it is to control ceiling fan and light

the existing switch does not have neutral .but I found there are 3 bundle wire. I choose one of them with white/gray color as my neutral

when I wire as above, it turns out it does not work. No lights on the switch. press the switch does not able to control light. the other existing switches works as expected

this is switch box. picture

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in terms of existing switch information. I think the left one is not 3 way switch.  the middle switch seem like does not control anything. the right one is controlling other outlet in the room.

I already tried switch the two hot wire for the kasa wiring. no luck

where could I did wrong? should I try another neutral wire from the bundle.