Creating a sub account didn't work for me (should it work immediately?).
So I tried something else.
I uninstalled the VERIZON FIOS MOBILE app.
Restarted my device (I don't know if that part was necessary).
Since I didn't have the VERIZON MY FIOS app installed yet, I installed it and signed in with My Verizon username and password with no problem.
I then re-installed the VERIZON FIOS MOBILE app.
This time when I went to sign in to the mobile app, it already had my user ID listed in that field and I simply had to sign
in with my password.
I was able to view some of my recorded shows on the device (while at home).
I just have to wait to see if it works next time I'm away from home.