My Smart Keyboard has stopped working

Remove the iPad from the Keyboard - and carefully/gently clean the smart connector contacts on both the iPad and keyboard with a soft pencil eraser (a drafting-film eraser is ideal). Ensure that the contacts on both iPad and keyboard are dirt and dust free - and all debris from the eraser have been removed - before reconnecting the two.

If you can't connect your iPad to your Magic Keyboard, Smart Keyboard, or Smart Keyboard Folio - Apple Support

If the problem persists after cleaning the Smart Connector contacts, try a forced-restart - as this will often clear an isolated software issue:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

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.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.