To make sure have have a great experience with the app, we do not recommend using Bluetooth headphones in Simply Piano. Bluetooth does come with delays and these vary across different headphones. We do hope to support Bluetooth headphones in the future though. In the meantime, we recommend connecting your phone/tablet to wired headphones.
While we do not support Bluetooth MIDI in Simply Piano, we have seen many of our learners successfully connect to Simply Piano with it. If you have trouble connecting to Simply Piano with Bluetooth MIDI, try connecting to another app that does support it (for example GarageBand) and then open Simply Piano.
Have more questions? You can talk to us through the app. Tap on Menu > Settings > Send Us Feedback / Contact Support :)