A few things to check:1) Did you build the app as a preview app? Make sure you checked the box for that on the first tab of the App Builder screen.2) If you didn't build as a preview app, did you publish all your content?3) Are you sure you built the app against the same project as your content is in?4) Did you make one top-level collection or two? If you made two, is there content in the appropriate top-level collection for the device you are testing on?Neil