warning: remote HEAD refers to nonexistent ref, unable to checkout

I am struggling for so long time, everytime getting different errors

I digged up my backup and started from scratch. Still not working.

On the (linux) server (directory contains already files):

 cd bin
 git init
 git annex init server
 git annex direct
 git annex add .

Then, on the Windows client:

 $ git clone ssh://me@server/srv/data/bin bin
 Cloning into 'bin'...
 warning: remote HEAD refers to nonexistent ref, unable to checkout.

What's going on here?

EDIT: Of course, I would not ask if everything would work as expected. But the client repository in windows is always empty, no matter what I do (issueing git annex init, git add remote, git annex sync, ...) does not seem to help me ...

EDIT2: When I continue on the windows side (despite the warning):

 cd bin
 git annex init client
 git annex sync
 Permission denied (publickey,keyboard-interactive).
 (merging origin/git-annex origin/synced/git-annex into git-annex...)
 (Recording state in git...)

   Remote origin does not have git-annex installed; setting annex-ignore
 commit  ok
 pull origin Already up-to-date!
 Merge made by the 'recursive' strategy.


 ok
 push origin To ssh://me@server/srv/data/bin
    b79922f..4fe0505  git-annex -> synced/git-annex
    2f6a601..02a2603  annex/direct/master -> synced/master

 ok

But that's not true, git-annex is definitely installed on the server (it's just the Debian package and it resides in /usr/bin/git-annex). In any case, the client repository is still empty

EDIT3: Struggle, struggle, ...

Finally, for whatever reason, the client dir is not empty. What seems to be missing on the server was:

 git annex sync

but this is never written (also not in the walkthrough). Can anyone tell me if it's required and why?

Furthermore, even that I "see" at least the file references now, I am not able to get them:

 $ git annex get apps
 get apps/gitignore (not available)
   Try making some of these repositories available:
         10d0ffd8-f499-4b55-83e6-ff58cd98edc5 -- server

   (Note that these git remotes have annex-ignore set: origin)
 failed
 git-annex: get: 1 failed

That's an SSH remote, it is available! What is meant by that?