I am literally copying and pasting this question from another user because I am having the same issue.
My son has the Just Kids plan, I have Smart Family app to control his contacts & usage. He has many friends that do not have cell phone plans yet and only have email addresses to use their phones with wifi. The Just Kids plan allows 20 contacts and I put them in with the Smart Family app. The app only allows telephone numbers and will not allow me to put in email addresses of his friends that do not have phone numbers. How can I get those email addresses put in on the APP for trusted contacts?
Just Kids is a terrible plan, switch to Start Unlimited. Cost is almost the same and doesn't have asinine restrictions.
Smart Family doesn't even work properly on iOS.