What are the requirements for the first 90-day check-in for a Non-O visa in Thailand?

In the same situation I was told by immigration that first 90 day report had to be in person. Subsequently it can be online. The first 90 day report doesn't have to be in the same province that issued the extension of stay

You can try online reporting first. You can try a few times online even if rejected, and you still have time for reporting in person at the immigration office.

The system has kept being improved bit by bit. A while ago, the system gave you this kind of message, ""For further information, Please contact the Immigration Branch Office in your residence area"", always in the rejecting notification mail. (<- no way to find what's wrong, you needed to do try-n-error blindly).

But now, since a couple of months ago, the system is giving you a bit more specific reason for rejection, so you can try to fix that part and re-try. If still a no-go, you can go in person.

You can use the on-line report system after you made an account on this website.

You make the report between 15 days before and due date.

At the end of your current 1 year, during the last 45 days you can apply directly for a new 1 year Extension of Stay if you still meet all the requirements.