Sound issue when app is launched by Callkit

In iOS, I have implemented the incoming call function using Callkit.
However, when the app is launched in response to an incoming call when the app is not running, the operation sounds that should be played when the buttons are tapped and so on do not play though the voice of the call plays correctly. This issue persists until app is restarted.

When commenting out [action fulfill] that is executed when responding, the all sound now plays correctly.
However, it is recorded as a missed call in the phone app history.

Is there anyone with a similar issue? The Unity version is 2018.3.14.

Did you find a solution for this? I am having the same issue…