We want to test dev client and I can't host server for playing. I think the connection should go through steam, but "Initializing Steam client failed (steam_api64.dll not found)." How to fix?

You can't host a server.
The only options for the dev client is to play singleplayer missions.

If you build in debug mode, there are entries in config.xml that allow you to disable Steam functionality.

juanjpro wrote:If you build in debug mode, there are entries in config.xml that allow you to disable Steam functionality.

Thanks, it worked