If you are wondering why the call getting dropped after 3 hours then this might be a good answer for you.
it is a fail safe feature provided by 3CX. Let’s assume on of your users does not hang up/drop the call properly and let the active session for a while. It remains there and of course counting your balance usage 🙂 until certain period then i will be dropped by this feature.
You can adjust the setting as you want with very simple way:
Go to settings –> Parameter (default value is 10800 in second)
*10800 second = 180 minutes = 3 hours
Reference link: https://www.3cx.com/blog/docs/calls-end-after-3-hours/