We're not sure exactly what screen is not loading.
Did you have a screen called Signature ID where you chose 5 numbers at random and had today's date and your birthday? If so, was it right after that screen that you had the spinning circle?
Did you get past a screen yet that says "I am not a robot" that has a captcha? It may be that captcha screen that's not loading, unless you already saw it and got past it. Have you seen a captcha?
Or were you getting the spinning circle after clicking the orange "Transmit My Return" button? Or is it before you get to that final screen?
