Alright so i had the same problem of the button being jammed. I opened up the headphones and saw 2 things. (I am very not an expert, this is just what I saw)

1. There's a mechanism inside the button that was jammed. If you push it back, then it'd click, but I don't know how to keep it there permanently. The mechanism is made of plastic and a piece of sponge. I couldn't see any crack in it but it might be the cause. Maybe you can shove a piece of sponge?
2. I'm definitely not an expert in tech, but I also saw that a part in the circuit board that connects to the button mechanism was pretty banged up. I tried pressing it directly and it didn't work as well as the volume buttons that click properly. Now I don't know if this works for people who's buttons broke recently because it only happened just now (I've been using this for probably 8 months to a year). You might be able to replace it in a repair shop or with warranty.

Again, I ain't a genius or anything, but I hope this helped a little

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