I tried to press the button on Powerbeats Pro in other apps, like YouTube or Music, and it can correctly start/stop the media playback. I declared NowPlaying in my app and add command handler, just like the previous work around, I can correctly receive the command when pressing the button on bluetooth headset.

To add more information Pressing the talk button on system UI worked, meaning the Push to Talk framework should be setup correctly. I tried to make the Bluetooth headset in both HFP mode (audio session in PlayAndRecord) and A2DP mode (audio session in Playback), did not help in either mode and cannot trigger the transmission when pressing the button on Powerbeats Pro.