I have several ipads that have been upgraded to 17.0.3 but I need to be able to back them up to 16.6.1 version. We have apps that do not work currently on 17. I have downloaded the 16.6.1 .ipsw file and every time I try to use it I get OS cannot be restored on "iPad". Personalization failed. Any way to get an os file that would work?