In preplanning you need to buy extra money for heist, Part of them gonna be in room with the code, another - in locked room.

First you have to get to the boss arena. There is a room on the second floor with a piece of paper on the table. Interact with it - get the code - write it down or memorize it.

Next, to exit the arena you have to press the button in the room on the third floor. The timer will start but don't be afraid, there is plenty of time. Run back to the first part of the map. There you go through the locker room/machine room, then to the rest room and from there to the room with the projector. Now the buttons on the panel next to the door become available to press - enter the code.

Now all you have to do is open the cases in the money room, bag them and throw them out the window.

When you get downstairs and get in the boat, the helmsman should just crash into the bags or drive by. Collect them all!