When trying to restore my iPhone, I get message "the iphone could not be restored. An unknown error has occurred. (9)

See this for error 9. If you see error 9, 4005, 4013, or 4014 when you restore your iPhone, iPad, or iPod touch - Apple Support

madmam wrote:

I found some old iPhones in the cupboard, prior old kid's phones, and I'm trying to restore them/erase them, so I can recycle these. While trying to restore, I get message: the iPhone could not be restored. An unknown error has occurred. (9)

If you see error 9, 4005, 4013, or 4014 when you restore your iPhone, iPad, or iPod touch - Apple Support