Thanks for the reply, sberman. Actually, I had read numerous other discussion posts about this (and similar problems) as well as articles all over the web that recommended just that. But I had my doubts as I always keep my macOS systems up to date. Since iTunes is kept up to date via macOS upgrades, I was pretty certain I had the latest possible versions for my two Macs (iTunes 12.8.2.3 on macOS 10.13.6 High Sierra on a 21.5-inch, mid-2011 iMac and iTunes 12.9.5.5 on macOS 10.14.6 on a 2018, Retina, 13-inch MacBook Air). I tried the process on both and got the same “The value is missing” message.
With a little more research I did, however, figure out how to get past it. The other bit of advice I was reading was to put the phone into recovery mode, then iTunes would deal with it and I could restore it to factory settings. Either I was not reading correctly or the advice was not quite accurate because I was holding in the volume down button and the home button simultaneously but nothing was happening. In re-reading the Apple kbase article I linked to, I found the instructions for the iPhone 7 was to only hold the volume down button in while connecting the device to USB until the connect to iTunes screen appeared, which worked. I am now happily downloading an iOS upgrade that will be used to restore the old iPhone 7 back to factory settings.
It pays to read Apple’s instructions carefully.
