I noticed that on signing up to DoubleAgent my FreeAgent 2FA broke the signup flow. FreeAgent loses the ‘forward onto’ URL parameter when it handles the 2FA page!
Thank you very much for your report. I can reproduce the issue by typing a wrong authentication code before submitting a correct one. I will file it as a bug and let you know once we have a fix out. Until then, would it be possible for you to ask your user to retry absolutely making sure to enter the code right the first time?