Before you can host a game, you need to download it. You only need to do this once for each game.

Note: You need BYOND installed to download BYOND games. If you don't have BYOND installed yet, start here; or download the client directly if you already have an account.

To download a game, visit its hub entry, the web page where live games are shown. Then look for a "Download" link.

Image showing the location of the Download link on a typical hub entry.

Click the Download link. The BYOND Pager will start up and download the game. Once it has finished, Dream Seeker should launch with the game in singleplayer mode. You can close it for now.

Note: Not all games are available for download. If there is no Download link on the page, this means you have to wait until someone else hosts the game before you can play it.

Back to "How do I host a game?"

If you get an HTTP error, it means that there are issues on the server where the game file is stored. Try contacting the developer of the game. It is unlikely that anyone else can help you. It is simply out of their hands.
It's not a matter of want. In this case, it's not even a matter of usage rights.

The BYOND staff does not have the files. Only developers and those the developers shared with have game files.

Except for the specific games that they developed themselves, the BYOND staff does not control individual games. They couldn't even if they tried. They're a small operation. They just make the tools.
For future note, please make sure that the game is zipped through Dream Maker, Build > Package Files (first option if you want the game to be hosted by others without the source released).

Zipping through external programs, such as WinZip, may compress it in a way that DM may not know (I assume) hence the unzip failed messages.