This can be cheesed as early as Dawnshore, the first region in the game. There might be other opportunities to get it earlier, but this worked for me.
During a side quest called “Precious Light”, follow the quest line until it’s time to hand the luminous adra over to Sapiento in the Market District. Of course, this requires making choices throughout the quest that’ll keep the adra in your hands, i.e. not siding with the Trading Company, etc.
When he asks if you have the adra you’re able to lie by saying you do not, which prompts him to end the conversation by asking you return when you do.
Spam this deceitful loop as many times as needed and there’s an easy 15G.