Not SideFX, but from my experience:
Uploads are blocked by Itch.io engine. If you press Edit game, you'll see this message:
> Uploads are temporarily disabled because voting for Houdini Game Jam 2021 is in progress. You'll be able to make changes after the jam is over.
You can edit the rest of the page: add links, screenshots, improve the description and style of the page, etc.