To use this cheat you need to first locate a red lockbox.
You may get lucky when you tap on it and you get an item or coins, but most of the time you need three diamonds. If the box needs three diamonds don’t pay for it instead “tap out of it”. DO NOT TAP THE X in the corner doing this will make to box go away and you don’t want that. Instead click away from area where the game wants you to pay for the three diamonds and the pop up should go away. The lockbox should still be there and all you need to do is refresh their farm :).
The box should unlock when you tap it the second time and if not try again.