When i pull the brake it doesent stay - Bugaboo Cameleon Jogger

When you pull the brake lever up it does not lock but pops back down? If so undo the two screws that hold the lever assembly together. You'll see an inner button with a spring and the lever. The inner button has ratchet teeth that need to lock into matching teeth on the inside of the black lever holder. If these are worn you can reshape them with a small file or a rotary tool like a Demell. The lever assembly should be kept well lubricated with silicon spray to avoid ware on the teeth. It is the teeth shape that does the locking and not lubricating them wares them down.