Why doesn't my selfie stick work with my iPhone 6?

It's the kind of selfie stick that works by plugging into the phone audio jack. It works on my moms iPhone 6 but when I use it on mine, Siri starts taking or it says voice control and it doesn't allow me to take the picture when I push the button on the selfie stick. I should add that it sometimes works. But most of the time it doesn't. Usually, it works once and then when I push the button again to take another picture, Siri speaks or I'm prompted to voice control. Does anyone know how to fix this problem? Is it something that can be changed with my phone settings? Or is it the selfie stick? The selfie stick isn't an expensive one, I bought it at Señor Frog's while vacationing in Mexico. The instruction manual only explains how to place the phone on the selfie stick and nothing else. I would appreciate some help! Thanks!

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