error 4000, what could that be

See this Apple article: If you see an error when you update or restore your iPhone, iPad, or iPod

If you see an error when you update or restore your iPhone, iPad, or iPod - Apple Support (SG)

Guess you use a Windows PC, if so check als the AV & Firewall on the PC. 

Disable your AV & Firewalls temporarily while you restore & update your apple device.

If they are On, turn Off Hotspot & VPN. 

See this user tip→If you see Error 4000 updating your iPhon… - Apple Community

Try to update your iPhone using Wi-Fi instead of connecting it to your PC. On your iPhone, open Settings > General > Software Update and follow the prompts.