I think I read the wrong information as I just read it again on the website, I do state 15 days before and up to 7 days after but I think this is in-person, when I clicked to link for online report it does as you say only say 15 days in advance. Noted for next time. It didn't cost anything to do it in the office but cost me 1500thb as it's right next to the fresh fish market and we came home with lots of crab,shrimp and squid.
just been to IMMIGRATION office and the lady said can only do it online from 15 days before and not at all after the due date, that's different from what it says online
I tried to do my online report and it was rejected not sure why, some people say I did it too late but it states on their website 15 days before and up to 7 days after I bone my one on the Friday 13th and due date was the ,9th.