How do I add a new line to my debit 

I’m having the same issue. But, when I try to share my line with digits, it’s telling me I can’t because there’s no email associated with my account.  
 

So, I go back into my T-Mobile account and my email is there.  
 

Not sure how to get this working, as there’s no contact or profile settings I can find in the Digits app.  And the FAQ is useless.