Please be more descriptive, what is an "auto sell chest" plugin? btw this should probably have been made in requests: https://forums.pmmp.io/forums/requests/
How can a chest sell something? Please be more elaborate. e.g. Explain how a player pays, who gets the payment, how a shop is set up
This is a pretty standard plugin in the minecraft community, chest sell means that any item placed inside the chest gets sold automatically and the player receives the money. So I guess you need a config file with itemrice and an event or task that fires when the player places an item inside the chest.