The consensus among community members indicates that the first 90-day report must be completed in person at the immigration office, especially after reentering Thailand. While some suggest attempting to file online for convenience, it is generally recommended to go to the local immigration office for the initial report. Subsequent reports may allow for online processing.
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.
Good to know. I've been unsuccessful online unfortunately. (Even the second time). (A hotel filed a TM30 in my name so the one on file did not match) But going there in person was very, very quick.