One more wrinkle....
I pulled the SIM, cleared out some files and pictures and dumbed-down the 5S iPhone, also turning off wi-fi.
Then I charged the phone, and shut it down.
After powering it back up, and launching the MOTIV app, I get a popup that tells me....
Unable to Verify App
A connection to the App Store is required for the first launch of "MOTIV Audio" on this iPhone.
Please connect to the Internet and try again.
I have to turn on wi-fi on the phone to get the MOTIV App to launch successfully.
I'll leave the iPhone plugged in and charging, and make sure to fire up the app before I leave the house, to double-check its launch.