Device not supported error for iPad Pro folio keyboard

See >>> If you see an ‘Accessory may not be supported’ alert - Apple Support

If you are using a Smart (folio) keyboard, the alert is typical of a faulty folio keyboard. The electrical connections that pass though the flexible fabric hinges typically fracture - this usually resulting in errors and/or the on-screen notification that you see. 

The Smart folio keyboard itself is not repairable. The only remedy is replacement of the keyboard.

If your keyboard is within its one-year warranty, you should contact Apple Support for assistance; you will find the Get Support link at top-right of this page.  Alternatively, you can initiate a support case using the excellent Apple Support App.  If not already installed on your device, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

A further alternative is to visit the Genius Bar at your local Apple Store, where the technicians will be delighted to assist.  When visiting the Genius Bar, a reservation is recommended:

https://www.apple.com/uk/retail/geniusbar/

Force restart iPad

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.