A seller signs in and tops up your account for you.
Your username, not your display name. It is the name after the @ on your Roblox profile.
Encrypted, seen only by the seller doing your order, and deleted when the order ends. We never change your email, PIN or account details.
Find them in Roblox under Settings → Security → Backup Codes. With all 5, the seller can start without waiting for you.
For order updates and tracking, e.g. 012-345 6789.
For your receipt and a link back to this order.