Security apps or firewalls, among other things, are thought to be the most prevalent causes of iTunes error 9 on iOS devices, including the iPhone 6s Plus. These tools are primarily intended to block or prevent any security risks from penetrating the computer system. When you connect your iPhone to your computer, it will be recognised as an external device or storage media by the computer. External devices that are linked to the computer might constitute a security risk to the system. It is for this reason that security software is installed and enabled. Your iPhone might be a security risk if you have a firewall or security application installed on your PC. As a result, security software or firewalls perform their job of blocking it. Access to your iPhone through iTunes will then be blocked or halted, and you'll be greeted with the error 9.

A solid network connection is one of the most important requirements for completing software updates. iTunes may need to visit the Apple server to get essential resources when performing an iOS update or restoration. iTunes would be unable to establish a connection to the Apple server without a solid connection, and hence would be unable to complete the procedure. The iOS update or system restoration has been halted again again and is unable to complete.