Have you purchased a current (or at least a recent) model of iPad - or an older model? Not sure which iPad you have? Identify your iPad model.
Before performing a data transfer, the initial setup process will initially try to update the “new” iPad to the most recent version of iOS/iPadOS that the iPad model is capable of support. Here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:
- iPad1 - iOS 5.1.1
- iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)
- iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)
- iPad Air1, iPad mini2 and iPad mini3 - iOS 12.5.5
Newer models, not appearing in this list, are all able to be updated to the current version, iPadOS 15.6.1
These support pages should get you started with setup of a newly acquired iPad - and the methods of transferring your data from old to new iPad:
Set up your iPhone, iPad or iPod touch – Apple Support
Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support
Use Quick Start to transfer data to a new iPhone, iPad or iPod touch – Apple Support
If the donor iPad, from which you are transferring your data precedes iOS12.4, QuickStart will not be available.
“Transfer” is rather a misnomer. In reality, your data and setup is merely cloned to the new device. Nothing is moved or removed from the original device.
An alternative is to restore either an iCloud or iTunes backup to the new device:
How to back up your iPhone, iPad and iPod touch – Apple Support
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
Be aware that a data transfer requires the “new” iPad to have the same or more recent version of iOS/iPadOS than the original iPad from which data the data will originate. Put another way, if the “new” iPad has an older version of system software, the transfer process will fail.