Invalid position index error when creating item-source

I wanted to create new item source:

curl --location --request POST 'http://localhost:8080/api/item-sources' \
--header 'Authorization: Bearer XXX' \
--header 'Content-Type: application/json' \
--data-raw '{
  "code": "doi",
  "label": "doi",
  "ord": 0
}'

and got

{it 
    "timestamp": "2021-04-09 13:58:22",
    "status": 400,
    "error": "Invalid position index 0 (maximum possible: 3)"
}

However, it works when I set ord to 3.