You don't have to enable the Bluetooth connection in iReal Pro, only in your device's settings.
Here you find more info how to pair your Bluetooth device with your iPhone/iPad:

This will use additional battery drain, so turn it off again after practice if you do not usually need it on.

In case you have any sound issues and the first beat of the playback is missing, connect your Bluetooth speaker to your iPhone/iPad and send us a screenshot of your Bluetooth device's name that shows up in your iPhone/iPad's settings -> Bluetooth -> device name (tap on 'i' Info).