iPad failing to activate after updating to iOS 15

Its not particularly clear what you might have tried - so I’ll try to cover all the potential options…

If you are experiencing difficulties with (re)activation of your iPad, you may have more success if you connect your iPad to a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of macOS). Once connected to your computer, your iPad will be detected - and you should be able to activate using iTunes.

1. Make sure that you have the latest version of macOS or the latest version of iTunes.
2. Check that your computer has an Internet connection.
3. With the cable that came with your iPad, connect your iPad to your computer. Locate your device on your computer.
4. Wait while your computer detects and activates your iPad:

• If you see an alert that shows "Set up as New" or "Restore from Backup", it means your iPad is activated.
• If you get an error message that says the "activation information was invalid" or "activation information could not be obtained from the device", use recovery mode to restore your iPhone.

A restart of your WiFi Router and/or a change of DNS settings may also be helpful - and direct activation from the iPad itself may again be possible.

To restart you home router, disconnect power - then wait at least 30 seconds before restarting. When you router has rebooted (which may take several minutes), force-restart your iPad:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

For recommended DNS servers (configured at your home router and/or your iPad), you might choose one of the following Recursive DNS Providers (IPv4 and IPv6 addresses included below):

Quad9

9.9.9.9

149.112.112.112

2620:fe::fe

2620:fe::9

OpenDNS

208.67.222.222

208.67.220.220

2620:0:ccc::2

2620:0:ccd::2

Cloudflare+APNIC

1.1.1.1

1.0.0.1

2606:4700:4700::1111

2606:4700:4700::1001

Should it be necessary to escalate your issue to Apple Support, the quickest route to engaging with Apple Support will be via the  Get Support link at top-right of this page.

I had the same problem with a two year old 6th generation Ipad. It failed when a software update was done. I went through every solution the apple people here advise, even third party repair software. Nothing, dead ipad. Its PURELY apples fault.

theres only ONE solution, dont buy another Ipad. Ive owned countless apple products since they came out with earlyMacs. The company has gotten so large, they really dont care. They want you to remain brand loyal and simply buy a new device every year or two. If your perfectly good device fails due to THEIR error, you can always send it in to apple repair. And the cost will be far higher than a new device will be. Ive left the apple fold for this very reason. My suggestion to those who suffer these problems at apples hand, do the same.

Having tried everything, what information were you given by Apple Support when you contacted them - as recommended in the last step of my reply?

If suggested steps are unsuccessful - and you won’t accept the diagnosis that you have received - you have perhaps exhausted your available options.