bought Rocket League before the allowed to-play update, you Rocket League Items can overlook this limitation.
You can just exchange with players on a similar stage as you, but since Rocket League has cross-movement, you can sign in to any stage to see your tradeable.
things. There are a few things you can't exchange, including concealed Blueprints, things bought from the shop, and extra presents. Essentially, you can't exchange credits for Buy Rocket League Items credits or credits in vain. It must be credits for a thing, and just a single player can offer credits.