Mr. Strauss will ask for your help in collecting the money he loaned to other people during the main story mission Money Lending and Other Sins. When collecting money from the debtors, you can use intimidation, threats, or even violence to some degree but you’ll have to make sure not to kill them.
Sometimes you won’t get the actual money as payment but in other forms such as valuables. These collected funds and valuables needs to be contributed to the camp but don’t worry since you’ll still get a reasonable cut for your trouble. You're not required to bring home a collected debt immediately. So you can collect other debts then just deposit them to the camp's lockbox all at once.