Some Android devices may require you to manually allow additional permission on the device to enable the Record app to access and use the Bluetooth microphone.
If your device is showing that the Bluetooth microphone is connected but the app is not (e.g. its showing grey/orange/red on the Bluetooth icon) then follow these steps:
1) Go to Settings
2) Bluetooth menu
3) Find the connected microphone and go the settings
4) Allow calls and audio