For my Country "Vietnam" as soon as the case status "TRANSFER" you have to submit the DS-160 and create a UStraveldocs account and also register the mailing address for them to MAIL you a PKT3.
You CAN NOT pay for visa fee or schedule an appointment until you Received the PKT3 from the consulate.
that is what I have read from the Viet Nam consulate website. Some one please correct me if I'm wrong. thank you