Hello, quick question about the 90 days notification of stay.

I arrived in Thailand on 13 February 2021 (with an exemption of visa into a extension into a in-country ED visa). I have to count the 90 days starting from my arrival date, right? or from the beginning of my ED visa?

I try to do it online here : [members only]

But I stay stuck at the first page : when I click on "submit", it's just reload the page and not take me to "step 2". A bug in their system or I miss something?

Btw, it's the first time ever that I do a 90 days notification of stay (I live in Bangkok). Bonus question : what the fuck is the point of doing that??