I am trying to create a new row inside of a Notion Database, by using the Notion API. This works perfectly fine with the title and the differed properties (Date and Select). However I couldn’t figure out how to set the relation property.

Here the request I used:

{
  "parent": { "database_id": "7042416ba4854e4fb88a9807cb7a43a6" },
  "properties": {
    "Name": {
      "title": [
        {
          "text": {
            "content": "Titel"  
          }
        }
      ]
    },
    "Fällig": {
      "date": {
        "start": "Datum" 
      }
    },
    "Art": {
      "select": {
        "name": "Art" 
      }
    },
    "Kurs": {
          "type": "relation",
          "relation": [{
            "database_id": "293f5f5526844766aed973e2c13b421a",
            "synced_property_name": "Kurs",
          }]
    }
  }
}

And here the error:

{"id":"293f5f55-2684-4766-aed9-73e2c13b421a","created_time":"2023-09-16T12:47:00.000Z","description":[],"request_id":"c288b635-4cb0-4ad5-b7f4-f5cbf42ffecc","is_inline":false,"last_edited_by":{"id":"cd42b981-1ccd-4593-89a0-390d692544b6","object":"user"},"parent":{"type":"page_id","page_id":"c6ae7347-d6fd-4e8f-979e-5602bf9463a2"},"created_by":{"id":"cd42b981-1ccd-4593-89a0-390d692544b6","object":"user"},"url":"https://www.notion.so/293f5f5526844766aed973e2c13b421a","public_url":null,"title":[{"annotations":{"code":false,"bold":false,"underline":false,"italic":false,"strikethrough":false,"color":"default"},"plain_text":"Kurse","type":"text","href":null,"text":{"content":"Kurse","link":null}}],"last_edited_time":"2024-09-03T14:46:00.000Z","object":"database","icon":{"type":"external","external":{"url":"https://www.notion.so/icons/categories_gray.svg"}},"cover":null,"properties":{"Name":{"id":"title","title":{},"name":"Name","type":"title"}},"archived":false,"in_trash":false}

Thank you in advance!