The eXistdb package requires a small support app to be installed in the database instance you want to access. You should be asked if you would like to install the support app the first time the package is activated. If this fails for any reason, install it manually by going to the eXistdb dashboard. In the package manager, search for an app called Server side support scripts for the Atom editor package and install it. Most eXist users will be familiar with the first approach because this is how the in-browser IDE, eXide, works. (2) has advantages if you are working on an existing app, e.g. cloned from git. In this case, you deploy the app once, configure the automatic sync and continue to edit files in the file system. We'll cover this workflow below. See the section on Automatic Sync.