not active after iphone 4s purchased through ebay restore his machine

Hi Nguyễn Quốc Thành,

Thanks for using Apple Support Communities. Based on what you stated, it sounds like you purchased a used iPhone and are not able to activate it. Is it asking for a password to use the device? I would recommend that you read these articles, they may be helpful in troubleshooting your issue.

Get help activating your iPhone - Apple Support

Find My iPhone Activation Lock - Apple Support

Before giving your device to someone else, always turn off Find My iPhone to ensure that the other person will be able to activate and use the device normally.

Cheers,

Mario