There is no update of ios13

Please provide more details. Which iPad do you own? Provide the model number that can be found in Settings --> General --> About --> Model Number.

If you have the iPad 5th gen like your signature says, your device is eligible for iOS 13:

Try to update with iTunes on a computer instead.

Get help with iOS updates

https://support.apple.com/en-us/HT209571

Get help with over-the-air iOS updates

https://support.apple.com/en-us/HT201435

Get help with iOS update and restore errors

https://support.apple.com/en-us/HT204770

We have NO clue why.

Are you running iOS beta system software?

How much internal free data storage space is left in your iPad?

What iOS version is your iPad currently running?