A bank proposed this instrument to me and I am confused.

Lets say a bank offers you this “ Invest 200,000$ and we will guarantee you a 9% return. However, the 200,000$ will be invested in an index such that if the value of the index goes up, you will be benefiting from the increase and if the index goes down, you will not be exposed to any losses” How is this structure possible? Do they buy the index? Do they buy long puts and if so, wouldn’t they be paying premiums from their own pocket ? Any help is appreciated !