If you can't login to study goal on iOS and others can, try the following:
1) Make sure iOS is up-to-date. We have instances where login wouldn't work until the latest updates had been applied.
2) Try clearing the Safari cache:
- Go to the Settings and tap on Safari.
- Scroll down to the bottom and press Advanced.
- Tap on the option that says 'Website Data'.
- See how much space it is taking up and press 'Remove All Website Data'