The consensus from the comments indicates that the first 90-day report must be submitted in person, particularly emphasizing caution regarding the safety of sending passports by mail in Thailand. While one commenter mentions that mail submission could be possible under certain conditions, it is recommended to either do it in person or utilize an agent to avoid potential issues.
90 DAY REPORTING RESOURCES / SERVICES
Use the trusted Thailand 90 Day Reporting Service to get your in-person report done and mailed to you for as low as 375 THB (even if the online system doesn't work for you).
For immediate assistance, contact Thai Visa Centre directly via LINE at @ThaiVisaCentre or Email them.