Problems using the API in remote Web Server

When running an app, the code will use the file system of the machine it's running on. In the case of a web app, that's the server it's running on, so when you deploy it to your remote server, it will use that server's filesystem, and not your computer's.

If you want the web app to interact with files on the user's computer, where the browser is running, you'll need to develop a way for data to be sent between the browser and server. E.g., let the user upload files using a file input. That's outside the scope of Dropbox API support so I'm afraid I can't offer help on that though.