I am experiencing the exact same problem with my mini. I have not used it in over a year, but I recharged it and when I turned it on, it accepted my passkey but then went into activation lock. It asked me to enter my apple id and password. This I did, but it tells me that my apple id is incorrect. It is the only one I have ever used and when I log into iCloud, it's accepted. I went into iCloud and cancelled the 'find my iPad" facility, but on restarting the iPad, it came up with the same result. The only change that I have made since last using my iPad, was to change my WIFI internet connection from a ADSL router to a Fibre router. I don't know if that has any bearing on my problem. I bought the iPad new several years ago and no longer have the receipts, so if what I have read from the various replies above, it looks as though I may have to throw the thing away. I hope not as I really like it.