How do I use a bluetooth remote shutter or selfie stick with ProCamera?

Please make sure Volume Buttons are enabled by going to Control Panel > Settings > Volume Buttons and turning the option On.

Note: This setting is not available on iPhones with a dedicated Camera Control button (iPhone 16 and later). Due to the way iOS handles these devices/buttons, the Volume Buttons are always enabled there.

On principle, you can trigger ProCamera's shutter remotely via bluetooth if your third-party bluetooth shutter emulates a headset.

Also, please make sure you have the volume of your iPhone set to a mid-range position, not to minimum and not to maximum.
(In case you were using a headset or AirPods, please make sure volume is set to a mid-range position there as well.)