Thanks for posting in the Apple Support Community. I understand that your iPhone shows the 'this accessory is not supported' error message when you plug it in to the USB port in your car.
For help with connecting your iPhone to the USB port in your car, take a look through these steps:
If you're using USB Playback
- Restart your iOS device and your car.
- Connect your iOS device to a different stereo USB port (if you have one).
- Try a different Lightning to USB cable.
- Update your iOS device.
- Install any firmware updates for your car stereo.
Try playing audio from a different app. If you can't play audio from a third-party app, contact the app developer for help. If you can't play audio from an Apple app, contact Apple Support.
Get help connecting your iPhone, iPad, or iPod touch with your car stereo
If you're still seeing the error message after going through those steps, you may want to take a look at this section from the following article:
If an alert says that your accessory isn't supported or certified
These alerts can appear for a few reasons: Your iOS device might have a dirty or damaged charging port, your charging accessory is defective, damaged, or non Apple-certified, or your USB charger isn't designed to charge devices. Follow these steps:
- Remove any debris from the charging port on the bottom of your device.
- Restart your iOS device.
- Try a different USB cable or charger.
- Make sure that you have the latest version of iOS.
- Contact Apple Support to set up service.
If your iPhone, iPad, or iPod touch won't charge
Take care.