Hello matilda184,
Welcome to the Apple Support Communities! We see your iPhone is not responding and you have an alert about an accessory that is not supported. We'd like to help out with this one.
Your best bet is to try a force restart of your iPhone if it's unresponsive: Force restart iPhone
That should get you back up and running. For more information about the alert you're seeing, we recommend checking out this link: If you see an ‘Accessory may not be supported’ alert
Hopefully that will work for you! Let us know.
Take care.