purchased used ipad still has previous owners apple id. I've restored it but now I can't activate it.

If you're able to contact the person who set the lock, send themthis linkand tell them to follow its instructions.

If not, you can't activate the device but may be able to get it refunded. Apple won't remove the lock for anyone other than the original owner(assuming they're alive.)

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You can't bypass activation lock. Your only options are to either contact the previous owner or return it.