Can’t update iPad

Well, after reading this support article:--> If your iPhone, iPad or iPod touch won’t update, if the issue persists, try a different wifi network, or update it using a computer.

If the issue still persists, contact Apple Support directly, using this link:--> Get Support , or make an appointment and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location

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After checking it out, they'll give you all the available options.

Regards

Giulio

Is your iPad connected to a reliable and fast wifi network with internet access?