Original message:
Hello,
I would like to create an additional plugin allowing the sending of a private message to each purchase made by a player. how can i set this up?
good to you

There is a ShopkeeperTradeEvent which you could hook into to detect when a trade is made: https://github.com/Shopkeepers/Shopkeepers/blob/master/src/api/java/com/nisovin/shopkeepers/api/events/ShopkeeperTradeEvent.java