You can only get a total of 8 battlecraft leves every 36 hours. If you've already done all 8, you have to wait until the next leve reset.

If you're wondering when the next leve reset is, you can type

/clock

into the chat dialogue box and it will tell you how long it will be.

Your completed leves will stay in your journal until you replace them with new leves after the reset. At that point, you can exchange them for new leves.

Welcome to the game, and good luck!