Symptom
When using Aircall on your phone, either via our application or with forwarding your inbound calls, a user notices their phone does ring, but the sound drops in volume or it does not ring quite as expected for all calls.
Do not disturb or Focus isn't on for their iPhone, and their sound volume is set to the highest level.
Cause
This can be caused by the Attention Aware Features on iPhone X and higher.
This feature may lower your notification sounds on the phone when you are looking at the device.
Solution
To disable this feature, go to Settings -> Face ID & Passcode and toggle the Attention Aware Features off for your device: