I recently purchased a second hand iPad Mini 3, as an upgrade from the original iPad Mini. When I try to activate iMessage with my Apple ID, it will return that there was an error in activating. When I try to activate iMessage on the new iPad with my brother's Apple ID, it works. When I try to sign into iMessage with my Apple ID on another iPad, it works. The only thing that doesn't work is trying to sign into iMessage with my Apple ID on the new iPad. I made this diagram if it helps to understand I've tried restoring it in DFU, setting it up as a new iPad without any details, and it still fails to activate. I can't understand why my Apple ID won't work on this iPad, but the iPad will work with other Apple IDs and my Apple ID works on other iPads. Thanks!!