I bought a used iPhone 6 and I can't get it to connect to iTunes. When I plug it in I get the error message "iTunes could not connect to the iPhone “iPhone” because an invalid response was received from the device." I tried booting the phone in recovery mode and doing a restore but when I try that I get the error message "This device isn’t eligible for the requested build". I've tried following articles online but so far nothing has worked. Any ideas?