Can I use it without an account? Yes. Tap "Start as guest" on the first screen, pick a nickname, and you can try courses, runs and premieres.
Is my location sent to the server? The raw GPS coordinates of your runs are stored only on your device; the server and other runners receive only de-identified checkpoint records. However, if you explicitly choose "Publish course" when saving, that course's route is uploaded to the server and made public to other runners.
My run was marked invalid. A run is invalidated if you leave the course by more than 20m and do not return within 15 seconds (you get a warning first when you drift past 15m). Runs that start mid-course without passing the start point are also invalid.
I want to delete my account and records. You can do it right in the app — Profile › Delete account (permanently deletes account and records). Deletion removes your account, your server-side run records and event entries, and resets the data stored on your device. Entry-fee payment records are kept only in pseudonymised form with account details removed, as required by Korean e-commerce law. If you have already deleted the app or cannot sign in, email shimyup@gmail.com from the address you signed up with and request deletion. After identity verification we will process it within 5 business days and reply with the result. See also the account deletion page.