Can't log in to LINE from Disney Tsum Tsum

I recently got hooked on Disney Tsum Tsum. Logging in via the LINE messaging app lets you sync your game progress across devices and also gives you some free in-game coins so I thought I would try it.

I was able to get the app installed, but I have no idea how to log in to LINE from inside the Tsum Tsum game. It asks for an email address and password, neither of which I gave when creating my LINE account. It auto-sensed my mobile number and texted me a confirmation code and that was that; I never had to enter an email address nor pick a password.

Any suggestions?

The LINE app is usable by itself without ever setting a username and password, but if you want to log in to the LINE service from another app (like Disney Tsum Tsum), you have to set those up.

To do that, go to this location in the LINE app:

More > Settings > Account > Email Account Registration