If you're getting an HTTP error 403 while trying to access a file for your UE4 HTML5 game, it means that the server has denied your request to get to the file. There are a few reasons this could be happening, like the file having the wrong permissions, or there being an issue with the server's settings.

To fix it, you can try checking the file permissions to make sure you have the right access to it, and also double-checking the URL to make sure there aren't any typos. By doing these things, you should be able to get past the error and access your game's files on the server.