Invalid response from device?

Your iPad mini 4 is too new for either Snow Leopard, or iTunes 11.
If you need to do updates through iTunes, or a full restore, you will need a newer system, or simply a newer Mac.
Mountain Lion or newer will be good, as that will have iTunes at version 12.3 or later.
If your Mac cannot be updated past Snow Leopard, and you still need to restore your iPad, then you have some decisions to make, I suppose.
1. Replace your Mac with a newer model.
2. Upgrade OS X to at least Mountain Lion (OS X 10.8.5), or newer. If the Mac is too old to accept that update, then you have to decide if upgrading/restoring the iPad is important enough to replace your Mac.

 

Had the same issue with my iPhone when I updated to iOS10. No solution for it other than to get an updated machine. My older iMac (with Lion) and the older version of iTunes would not let me restore or even connect my phone to the iMac. Finally bit the bullet and got a new, refurbed iMac and managed to get my iPhone restored and connected properly. It was worth the money, by and large. I had been planning to wait till Apple updated the iMac line, but that pushed my hand. I wish you the best of luck.