Unclosed polygon: first and last coordinates must be the same

What the Information System does

It rejects them. "“Open” polygons. All polygons must represent closed shapes (i.e. the 1st coordinate pair same as the last)" is one of the common file errors (GeoJSON File Description, Common errors 4), and the definitions say "the first and last point's coordinates of polygons are the same" (GeoJSON File Description, Definitions).

A broken example

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "ProducerCountry": "CI",
        "ProductionPlace": "Open",
        "Area": 1.2287
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [-5.123456, 6.123456],
            [-5.122456, 6.123456],
            [-5.122456, 6.124456],
            [-5.123456, 6.124456]
          ]
        ]
      }
    }
  ]
}

What the checker reports for this file:

1. This polygon does not close: it starts at -5.123456, 6.123456 and ends at -5.123456, 6.124456. Every polygon must end where it began., line 27, column 13

Fix it in EUDRplot

1. Open the file in the checker. Every open ring is listed, with the gap between its first and last point.
2. Close them. Choose Close the boundary, or Fix N safe problems. The first point is repeated at the end of each ring; the enclosed area does not change.
3. Download. Open Download and choose GeoJSON file.

Fix it in QGIS

This is a problem in the text, and whether QGIS closes the ring for you when it reads the file depends on the GDAL version it uses, so do not rely on it. The fix is to repeat the first coordinate pair at the end of the ring. The checker does it for every ring at once, and confirms the area is unchanged.