I actually haven't tried that, because I'm using Citizens NPCs to open the page I want. I will give it a try later though, and see if it works for me.
You are trying to make a certain page open, when you type '/shop'? It seems to work for me. I opened /plugins/Shop/config.yml The second line says: MAIN_PAGE: '' Add your page name between the quotes, so it says: MAIN_PAGE: 'nameofyourpage' Reload the config with '/shop reload'