Unable to update my iPhone 6s Plus.

Check Apple Server Outages: Support - System Status - Apple

Prepare for iOS updates

Before any iOS / iPadOS update, please do the following

• You need to Identify your iPhone model - Apple Support
• It is also recommended that you either take a backup on iTunes or iCloud --> How to back up your iPhone, iPad, and iPod touch
• If you have a beta profile installed, remove the public beta by deleting the beta profile

Go to Settings > General, and tap Profiles & Device Management. Tap the iOS Beta Software Profile. Tap Remove Profile, then restart your device --> How to uninstall iOS beta software - Apple Support

Disable VPN

VPN or proxy connections might prevent your device from contacting the update servers.

Contact the VPN Service provider and disable it for the time being. In some cases, if the VPN server or network is configured to block certain domains or IP addresses, it might inadvertently block Apple's update servers. This could prevent your device from connecting to Apple's servers to download the update. Make sure that the VPN settings do not block Apple-related services.

Download Again:

• Get help with over-the-air iOS updates - Apple Support
• Remove and download the iOS update again

If you still can't install the latest version of iOS, try downloading the update again:

1. Go to Settings > General > [Device name] Storage.
2. Find the iOS update in the list of apps.
3. Tap the iOS update, then tap Delete Update.
4. Go to Settings > General > Software Update and download the latest iOS update.

If you don’t see the update in the list of apps or if the issue happens again, you need to update your device with iTunes.

Try updating iOS after each step.

• Try to Forget the WiFi network and add it again
• Try another WiFi network 
• Toggle Set Automatic Update off and then on
• Reset your network settings
• Force restart your device
• Remove any beta profiles, if applicable

Corporate Device check

If this is your corporate iPhone, it is important to reach out to the system administrator of your corporate. They will be able to assist you with any issues or concerns related to your device.

However, if it is your device, there are a few things to consider. Firstly, check if you have any profiles installed by your corporate, organization, enterprise, or school management. These profiles are typically used to manage certain settings or restrictions on your device.

If you do have a profile installed, and you no longer wish to keep it, you can follow the steps provided by Apple to remove configuration profiles on your iPhone. By doing so, you will eliminate the profile and its associated settings from your device. Install or remove configuration profiles on iPhone - Apple ...

In case you need further guidance or encounter any difficulties during the process, it is recommended to contact the system administrator of the organization that provided the profile to you. They will be able to assist you in removing the profile or addressing any concerns you may have.

Try updating using iTunes/Finder

• If everything fails: - Use iTunes or Finder (for macOS Catalina+) to update your device instead of over-the-air
• Get help with iOS updates and restore errors - Apple Support
• If you see an error when you update or restore your iPhone, iPad

Check internet connectivity.

Your device is probably not connected to the internet. There are a few steps you can take to verify the connectivity of your device.

You may test the internet connectivity in two ways...

1. Firstly, you can open a web browser on your device. When you open a web browser, the initial page that loads is typically based on your browsing history or cookies. To further confirm the connection, you can tap on any link on that website. If the link opens and displays the corresponding content, it confirms that your device is indeed connected to the internet. See the pic below
   1. 
2. Another method to check internet connectivity is by opening a specific application that requires an internet connection. WhatsApp is an example of such an application. When you launch WhatsApp, it immediately attempts to establish a connection with its servers to synchronize your chats and display any new messages. If you can see your chat conversations and receive real-time updates, it indicates that your device is connected to the internet. See the pic below
   1. 

Connecting to Wi-Fi is the initial step, followed by establishing an internet connection.

However, it's important to note that connecting to Wi-Fi does not automatically guarantee an internet connection. If you are unable to connect to Wi-Fi, the issue may stem from settings on your iPhone or the router/modem.

On the other hand, if you are unable to establish an internet connection despite being connected to Wi-Fi, the problem is likely related to the settings on your router/modem. In such cases, it is advisable to promptly contact your Internet Service Provider (ISP) for assistance.

Check Router Settings

Check your WiFi Router / Modem for --> Recommended settings for Wi-Fi routers and access points ...

Connecting to Wifi is the first part and then getting connected to the Internet is the second

1. If you connect to Wifi, doesn't necessarily mean you are connected to the internet. If you are not connected to wifi could be a problem with iPhone settings or Router/Modem Settings
2. If you are not connected to the internet is the sole issue of Router / Modem Settings. Contact your ISP immediately

Contact ISP or Carrier

For your Internet connection.

• Over Cellular: contact your Carrier (Cellular Service Provider). The agency that issued the SIM to you
• Over WiFI: Contact your ISP (Internet Service Provider), the agency that provided the Internet Service on your Modem/Router to you

However --> Connect iPhone to the Internet - Apple Support

Update options:

There are only 2 ways to update an iOS/iPadOS. Know how to...

• Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
• Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)