Here is a link how to connect your device to Bluetooth:

Within your Bluetooth connection, check the settings in case the audio playback of iReal Pro is skipping.  Downgrade the connection to audio. If you still have issues, contact us directly with your device info.

In iReal Pro version 8.3:
In case the playback position marker is lagging, you might need to adjust it.
Tap on:
More -> scroll down to Advanced audio settings -> Bluetooth lag adjustment

It is caused by a delay within the device sending the audio output through Bluetooth.
By default, it is set to 500ms but different devices may need a different setting.