If your device supports bluetooth accessories, then this keyboard should work with it.
B046 Multi Device Bluetooth Keyboard
Multi-Channel: connects 2 devices at the same time, easy switching channels
Rechargeable: built-in 180 mAh battery, 2 hours of charging standby for 6 months
Portable Design: compact but steady enough to mount your tablet/ phone on it
Universal Compatibility: Windows, Mac, iOS, Android, any Bluetooth device
The slot is 10 3/4 inches long. It works with iPhone SE and iPad mini 3, it should work on your iPad mini 3.
Thru the bluetooth connection.