Problem/Bug PlotSquared and ChestShop problem.

On my prison server I am using PlotSquared as my plot plugin for players to build and I wanted them to be able to create shops. So I added ChestShop. Everything is good with ChestShop but when players try to buy/sell from other peoples plot that they do not have access to they get this error message:

Error: https://gyazo.com/41cb94ba9576d43edd409a3ca3a8f9d1 (Screenshot of chat after left clicking sign)

I tried to set both use and break flags to allow but the player was still not allowed to sell/buy.