You found a rare loot box! Wow! You can see what's inside by opening it from your inventory, after you opened the loot box all currency and items should be in your inventory.
rare loot boxes are hard to find, with a very low spawn rate and rarely being given out in events, making these loot boxes tricky to obtain, while its not impossible it might take some time before you run into one. Rare loot boxes tend to be a little more empty BUT the few items they hold are more valuable on the game market.
Loot boxes cannot be sold but can be traded or gifted to other users.