I was playing Civilization V Brave New World and a notice popped to the right saying that the city-state of Genoa will appreciate gold investment at the moment (20 turns remaining) and will return 50% profit.
I thought if I give them a huge amount of gold like 3000 gold they will return 4500 to me. After some turns I noticed that I didn't get the big flow of gold. I checked the city-state and noticed the gold investment quest is not there anymore.
How do these gold investment quests work?