Found this on Sweetwater:
Works great, but non-obvious connection
This plug works great for using my Reface CS as a MIDI controller for my iPad synth apps. But, this does not connect to iOS devices like other Bluetooth products like speakers. You need to open up the synth app and go MIDI settings there and find Bluetooth MIDI choosing that you can finally get the synth w/MD-BT01talking to the app. Seems to work with no delay and minimal movement of knobs/sliders.
If you still cannot get it working, please provide a screen shot of the MDP2 connections page showing your connection status to the BT adapter.