Accessory not supported

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. As you appear to be within your one-year limited warranty, you need to contact Apple Support or your retailer.

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/

The Apple smart keyboard cover has a flaw where the internal connection of the magnetic smart connector buttons becomes intermittent due to constant flexing of the case between the metal connection on the bottom side of the iPad and the keyboard.

This connection will only get worse as time continues.

There is no fix for this other than another brand new smart keyboard cover.

Apple's warranty period on its accessories is only 1 year and Apple’s extended warranty program for these smart keyboards ended some time, ago.

If this “accessory not supported” message continues or gets more frequent, you will need to, eventually, replace this smart keyboard with another new one, if still available by Apple or from another third party seller.

Sorry & Good Luck to You!