Having trouble uploading HTML zip

Hi, just wondering if I'm the only one encountering the problem. We're working with Unity and we have the build settings set up the same way the Embedding Guide specified. The index.html and other folders are at the root of the .zip and the game throws the following error in console: "index.html:114 Ignored call to 'alert()'. The document is sandboxed, and the 'allow-modals' keyword is not set." I tried uploading the same .zip to itch.io and it worked without any issues.