感谢回答！
我的情况是2020年2月我已经缴费了，但是因为中美断航，父母没有过来。最近父母重新在广州面试才过来的。我的问题是还需要重新缴费吗？我查了一下，他么的IOE number还是没有变的，所以我assume他们不需要继续缴费了，但是向和老师confirm一下，谢谢！
-It seems you paid the visa application fee and the other fee related to the immigrant visa application, not the immigrant fee which is additional fee not related to the visa application. Immigrant fee only can be paid after they got the immigtrant visa. They need to pay this fee after they got the immigrant visa before thye enter US or after they enter US using the immigrant visa. Otherwise, they will not receive the plastic green card. Read this link carefully for the immigrant fee and how to pay it:
USCIS - Immigrant Fee - USCIS Immigrant Fee
