I don't know if it's the plugins fault or what's the deal, but the placeholder doesn't work. This is the documentation from the wiki:
Where [currency] is your custom currency identifier (equals to the currency file name).%coinsengine_balance_[currency]% - Displays player's currency balance formatted by currency settings.
Where [currency] is your custom currency identifier (equals to the currency file name).%coinsengine_balance_[currency]% - Displays player's currency balance formatted by currency settings.