bee can fly

Make sure your account status is 13+ and not <13. This status can be seen at the top right of your username. Example: my items: 13+
Before buying, make sure you have the Builder Club (BC) and small limited items
Order merchandise and make payment, then wait until the seller processes your order
After your order is processed, the seller will send a Trade Request to the nickname you entered when placing the order (make an appointment with the seller regarding your small limited item)
You will get a message notification on Roblox, which contains a Trade Request from the seller
Click the Trade tab, then click View details
Check whether the items offered are as ordered (also your limited small items). If so, click Accept
If it is correct, click Done on my items to complete your order