I have always done mine online. But unfortunately i went to Australia for a month, got back on 27th August, so my 90days was ready to do. Got online this morning and tried to do it online, rejected. I had to go in, with all the new paperwork, and submit it. So if you leave Thailand and return you have to go in to do it. This is Pattaya Immigration. If you dont leave, no problem, can do online. When i have to it next time, no problem doing online.