It may already be too late to add AppleCare+ coverage. This insurance product, should you wish to benefit from its benefits, must be added within 60 days of initial purchase.
If AppleCare+ cover is not included in the original device purchase, subsequent addition of this cover is contingent upon the device passing a remote diagnostic test. If your iPad has developed a fault between purchase/activation and the attempt to add AppleCare+, you may have lost the opportunity.
Whilst AppleCare cannot be added after a fault has developed, you will still be able to make a claim under the one year limited warranty included with your iPad purchase.
You will need to seek assistance or advice directly from Apple Support, or from the Genius Bar at your local Apple Store.
Apple Support can be contacted using the Contact Support link at top-right of this page. Alternatively, you can raise a support case using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:
https://apps.apple.com/gb/app/apple-support/id1130498044