How do use a shapefile with polygons to crop a pointcloud by using the filters.crop in PDAL?

I tried the following syntax:

   [
    "input.laz",
    {
    "type":"filters.crop",
    {
   "type":"ogr",
   "datasource": "Buffers.shp",
    "drivers":"ESRI Shapefile"
    }
    },

    [...]
    ]

but it results in a syntax error:

PDAL: Pipeline: parse error at line 5, column 3: syntax error while parsing object key - unexpected '{'; expected string literal

Line 5 is the opening "{" after the "type":"filters.crop" line

I did not find any examples and documentation just mentions that "ogr" is an json object. I can't figure out how to formulate that it works.

Any help appreciated!

Roland