Node-Red to Slack attachments

Hi Guys,

I'm new here and working with node-red for half a year or so. I like it very much and still learning alot. But I have a problem. I'm sending my notifications and images via Pushbullet and that worked like it should. But I want to also be able to send them to Slack. Normal message work fine with a Slack Bot. But when sending a local image or other attachment I receive: error: "no_file_data".

I use the function node "slack web out" from: node-red-contrib-slack v2.0.0

msg.topic = "files.upload"
msg.payload = {
    channels: "#general",
    //title: "this is a test",
    initial_comment: "test",
    file: "@/dir/dir/node-red/image.jpg"
return msg

Is there somone that could help me with this one?

Sorry if I put this in the wrong forum.