I have tested this one extensively because it is broken for me. I made a save with 13 coins in front of the fountain. I throw 7 coins at the mirror up on the left side and 6 on the right side and it unlocks every time.
However, this objective is broken for me still (has been since Bangkok came out). After completing it and exiting or completing the level, the objective reverts to incomplete.
I also had a problem where I didn’t get the gold trophy for Colorado, but that fixed itself when the January 31st update came out. However, this problem has still never resolved.
@Travis_IOI please look into this further if you could. Also, my objective for completing the Mallory Misfortune Escalation (first one set in Colorado, don’t have the game in front of me right now) also reverted to incomplete after the January update despite me having the trophy for completing said Escalation.