Locked iPhone triggers JBL Pulse 3 pink light

Good evening everyone!

I just purchased my JBL Pulse 3 and realised when my iPhone screen is locked and I’m listening to some music, it triggers the Pulse 3 pink lights like if I was turning the volume up/down.

That doesn’t seem to happen when my phone is unlocked. I tried reseting my JBL but it did nothing. Does anyone know if it’s a glitch? How can I fix it? Thank you.