Can I check in for the 90-day report in Thailand by post or online?

You can report your 90-day check-in in Thailand either in person or online. To do it in person, you can visit your local Immigration Office between 15 days before the due date and 7 days after. Some offices may allow reporting by post, but it's advisable to check with your local office for their specific procedures. Alternatively, you can report online via the official TM47 website after creating an account, also within the same time frame.