This Apple Account is not valid or not supported.

That usually means the Apple Account or password is incorrect, or doesn’t match what is associated with the Activation Lock set on that iPad.

Contact Apple Support: Contact Apple for support and service - Apple Support

If you have he original purchase receipt: How to remove Activation Lock - Apple Support

Hello,

For help with an invalid/not-active/not-supported account you need to contact Apple.

To reach Apple Support for an account issue:

1. Click here --> https://getsupport.apple.com/?caller=cups&PGF=PGF63005

2. Select: Disabled Apple ID

3. Select: ”The Apple ID is not active" alert

4. Select: “Continue”

5. Select a chat or telephone call option.

or:

Contact Apple for support and service by telephone --> Contact Apple for support and service - Apple Support