Developer Token Not Working When Using UI Element

I thought there was something wrong with my app when trying to implement the Content Explorer UI Element because I put in my developer token and it said there was a network error. However, I went on the codepen for the UI Element, followed all of the directions (including putting the codepen domain in CORS) and plugged in my developer token and used '0' as the file ID and it still gives me the network error. I even tried it on two different browsers and two different wifis and nothing works. If anyone has any tips that would be great!