I flew SQ 608 from Singapore to Incheon on July 28, 2023. I sat in seat 56A (I was also happy to be sitting alone in 3 seats.) So I slept in 3 seats. Since the flight was at night, and I was very tired.The plane took off at night at 00:10 AM and the lights in the cabin were turned off. All passengers on the plane were asleep. But the fact is that from my backpack (blue-yellow Samsonite) 600 USD was stolen from the wallet that was in my backpack while I was sleeping.The money was taken out of my wallet and then the wallet was put back into my backpack. Could you check the security cameras inside the plane.