What should I do if I forgot a document while applying for a Thai OA Visa online?

Did the visa site tell you which Embassy/Consulate to send it to?

It happened to me earlier in January. If you look at your application on line it will tell you what is happening. On mine it said awaiting extra document, they had told what they wanted and I sent it less than 10 hrs later I had my visa.

You should not submit again, as that would require you to pay again.

You also cannot submit additional documents through evisa once your application has been submitted, even if the embassy requests additional documents. If they have any issues they will e-mail you and will request you to e-mail them back with what they are asking for. Keep an eye on your e-mail as well as your spam filter folder.

You should have plenty of time if you're not flying until March. Washington DC isn't known to be a very slow embassy.

If you absolutely must contact them, try using Facebook messenger. I know it sounds weird but many of the embassies reply through Facebook better than other methods. You must be very strategic about how you do this though, as you must remember they are very busy and also not native English speakers.

Just send a single Facebook message and include everything in that one message.

"Hello, my name is xxxx, passport number xxxx, OA Visa application number xxxxx submitted on xx/xx/xx

I did not attach the 2nd page of my required insurance when I submitted my visa application. I want to know if this will cause any issues with my application.

Thank you"