Stumped by 60377 Syncing.

I'm not quite sure how to get the lego train controls for the 60377 train to actually work reliably. I've watched videos on it but when I press the button on the train itself followed by the button on the control it flashes purple, then flashes white, and then it never turns to green. I've gotten it to work once briefly but then I've never gotten it to work since then. What am I doing wrong? I'm using the remote control and not the app at all. Thanks. submitted by /u/Cysteine_Chapel64 ...