After struggling with this for way too long..
I thought I'd share my experience with setting up DIGITS on my LG G5. The instructions provided by T-Mobile have some missing steps. I've added the missing parts in RED
DIGITS comes built in on several T-Mobile branded Samsung and LG phones. To log in to DIGITS on a supported T-Mobile branded phone:
That's how I got it to work on my LG G5
Manage your T-Mobile account