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We have paid for "I-130, I-864 & DS-260". I read somewhere says "Immigration fee" needs to be paid after Visa granted during interview, and I-485 fee (plus biometics fee) needs to be paid after being admitted into US.

-You can pay the immigration fee to USCIS after your parents get the immigration visa before they come to US. So, they can get the green card very soon wfter they enter US. The immigration visa approval document will tell you how to pay this fee.

Now for my parents' interview in Guangzhou, will there be any other fees to pay?

-No. 

Thanks.