Hello, We are building an online marketplace similar to 'letgo' inside shoppify, and wanted to build a third party app that allows the buyers and the sellers to have a chat when buying and selling their products. This chat will be available before even buying the product, and allows for negotiating prices and such. Our platform is a website that is exclusively focused on college students for them to sell in a secure enviorment, but we are missing the key component of the chat in order to launch. There are no plugins within shoppify that allows us to do what we want, so we come here for help. Thanks.