How to add a raster layer to Geoserver via the REST-API?

Question

I want to automatically (via script) add new TIF-files on the harddrive to Geoserver as a new layer. I use the REST-API for that.

In the first step I added the TIF as a coveragestore, and that step works. So I use this JSON:

{
    "coverageStore":
    {
        "name": "test123",
        "type": "GeoTIFF",
        "enabled": true,
        "workspace":
        {
            "name": "TEST"
        },
        "url": "file:\/\/\/data\/test123\/test123.tif"
    }
}

I add that via wget and that part works:

wget --user=test '--password=test123' --header='Content-Type: application/json' --post-file=coveragestore-test123.json 'http://localhost:8080/geoserver/rest/workspaces/TEST/coveragestores'

So far it s fine. But now I want to publish that as a layer, and that doesn't work. My JSON here looks like this:

{
    "layer":
    {
        "name": "test123",
        "type": "RASTER",
        "defaultStyle":
        {
            "name": "TEST:style123",
            "workspace": "TEST"
        },
        "resource":
        {
            "@class": "coverage",
            "name": "TEST:test123"
        }
    }
}

And I send it with this:

wget --user=test '--password=test123' --header='Content-Type: application/json' --post-file=layer-test123.json 'http://localhost:8080/geoserver/rest/layers'

It comes back with an HTTP-error 405.

What do I do wrong?