With respect, more details help identify issues…
What audio interface are you using?
Are you plugging in your earbuds (the one with the built in mic) to the interface or the iPad headphone jack?
In general, it’s an iOS feature that the most recently connected audio device takes priority. So the order you connect your audio interface, and the earbuds, makes a difference. iOS sees a new microphone (your earbuds) and that becomes the default audio input. Not a Cubasis issue really…