iPad says the wifi password is incorrect

If WiFi password works with other devices, whilst perhaps counterintuitive, a restart of your WiFi router will very likely resolve the issue:

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:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

What happens if you connect your iPad to a different wifi network? (borrow one from your friends/neighbors, or go to a public wifi place, or to an Apple Store or Authorized reseller).

If it works, the problem might be related to your modem-router.

Tap on the "i" in blue circle on your Settings>Wifi>[your network], then "forget this network".

Restart your modem router, and wait for its complete autoconfiguration.

Check again your modem-router password.

Reconnect your ipad and re-input that password.

If it doesn't work, try this procedure: Settings>General>Reset>Reset Network Settings, bearing in mind that this process also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before, but NO other data is affected. When done, restart the iPad.

If the issue still persists, contact Apple Support directly, using this link:--> Get Support

Regards

Giulio