Try another WiFi network instead of whatever network you have been using.
Or maybe Reboot the iPad and try again.
Reboot the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons
Reboot your router - unplug it from power for about 30 seconds and then plug it in again.
You can try resetting all settings. Settings>General>Reset>Reset All Settings. You will have to enter all of your device settings again.... All of the settings in the settings app will have to be re-entered.
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