Im having this problem today :(
Thanks for getting back to me. Just tried it again and got the same message. So basically I am creating a WEB GL app from Unity. Zipping up that folder and uploading the zip. I have a game on here already and tried to copy the same settings but sadly doesn't work. Here is a screenshot of my settings https://gyazo.com/9b1bef1ede1e08bda8bce668ca797387. The game is Infinite Drift. It does look different when I upload it compared to my other game as it has boxes I can tick next to the download which the other one doesn't. Ive tried checking the boxes but still doesn't work. Any help much appreciated.