What should I do if I lost my appointment slip for my 90-day report in Thailand?

If you've lost your appointment slip for the 90-day report in Thailand, you can file your report online between 15 days before and 7 days after your due date, as long as your personal data is accurate in the immigration database. Alternatively, you can report in person at the Immigration office within the same time frame. It appears that some users have reported difficulties with the online system, but it can work if approached correctly.