As suggested by the error, you would be best advised to wait a few hours - and then try again.
If any of Apple's back-end servers are offline or unavailable due to a network routing issue, you may see this or similar errors. In such circumstances, your only option is to wait.
The only other course of action is to restart your iPad - this having no negative impact for your iPad, but may clear a local network connection issue:
Force restart iPad (models with Face ID or with Touch ID in the top button)
If your iPad doesn’t have the Home button, do the following:
- Press and quickly release the volume button nearest to the top button.
- Press and quickly release the volume button farthest from the top button.
- Press and hold the top button.
- When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)
Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
