If an app tries to access the microphone while the microphone is already being accessed, it fails.
How can I make two or more apps access the microphone at the same moment?
Simply you can't. because microphone just like camera is a hardware part of the phone and it's drivers connects to only one source, there is a way to make this work but it will be difficult, by using an app to transfer the audio came from microphone and stream it to another app.
It was possible in earlier versions of Android. And I find the same problem, too. Using the third-party apps seems to fix this problem.
From www.androidpolice.com; Privileged apps have higher priority than ordinary apps. Apps with visible foreground UIs have higher priority than background apps. Apps capturing audio from a privacy-sensitive source have higher priority than apps that are not. Two ordinary apps can never capture audio at the same time. In some situations, a privileged app can share audio input with another app. If two background apps of same priority are capturing audio, the last one started has higher priority.
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