Ipad mini is definitely a no go, but the iPhone 7 plus is recommended.
What was the media on the sd card ? Occasionally you get the odd photo on a new drone, where the camera has been tested in the factory, but if there's anything else, it's definitely been used. (You don't say whether Amazon sold it as new or used).
The registration process starts when you first connect and turn everything on...the app asks for the email and password that you have registered with DJI to set up your account, and asks you to give the drone a name. Until you do that, it won't let you start the motors. If you didn't get that, it's a fairly definite sign that the drone has already been registered by someone else. You can check if the drone has already been named by going into General Settings in the app when everything is connected (tap the three dots at top right of the main screen), and scroll down to the bottom....you should see 'Device Name", and tap on that. Also, the last item is "About", and if you tap on that it will tell you the versions of everything installed.
If it has already been registered and named, and if Amazon sold it as new, I would think you have a good case to ask for a replacement.
None of the above answers your original enquiry, but I'm left wondering whether someone else had the same problem, and returned it to Amazon. The only other suggestion I have, is that maybe you could contact the DJI helpline to see if they can sort it for you.