Based on several posts on Twitter, it seems that around the world are reporting not being able to connect their phone to their vehicle or, in some cases, not even being able to start the car.
The reports mention an unexplained "500 Internal Server Error," which is, unfortunately, a pretty generic error. The existence of he outage appears to be corroborated by the website DownDetector.com, with 74% of reports of outages referring to the app. Tesla boss Elon Muskresponded to one user that he was checking on the issue, but no resolution has been announced as of the time of publication.