It's simple: Each of your goals has its own QR code with a unique reference number. You can find it in the app by selecting your desired goal and tapping on "Pay in". Either scan this QR code with your banking app or enter the QR reference number manually. This ensures your money automatically goes to the right place.

A quick note: Once your money is invested in a goal, it cannot be moved to another goal. It would have to be sold and then reinvested in the other goal.