It is possible that your WiFi router is unexpectedly blocking access to some internet/server resources - which might be resolved by a simple restart of your router.
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 using the procedure already described.
If you continue to experience difficulties, I recommend that you seek assistance directly from Apple Support - as you may need assistance with your AppleID account. You’ll find the Contact Support link at top-right of this page.
Please let us know how you get on.