I am currently in-country in KutRang... I already registered my wife's house and was trying to use the government site [members only]/ to do my TM 30 check in. Well, that site flatly refused to accept my data. I had used it before, but this time no go. I think something perhaps that it required an arrival number, but they no longer issue those. Anyhow... a couple of google searches and I found [members only]/ which gives 4-5 free registrations. I provided my current creds to the thai immigration site, uploaded my passport picture and about 30 seconds later was finally checked in. Perfect!
TLDR : Answer Summary
The user faced difficulties in checking their TM30 registration on the official Thai immigration website, speculating that it might be related to the absence of an arrival number. After searching for solutions, they discovered a third-party site (tm30.io) that facilitated a quick check-in process. Comments included potential issues with browser translation functions and concerns about the credibility of third-party registration sites.