curl --request POST \
  --url https://forgegames.org/api/item-instances \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '{
  "itemId": "<string>",
  "itemAttributeInstances": [
    {
      "itemAttributeId": "<string>",
      "value": 123
    }
  ],
  "userId": "<string>",
  "userSpaceId": "<string>"
}'

{
  "id": "<string>",
  "itemId": "<string>",
  "teamId": "<string>",
  "createdAt": "<string>",
  "updatedAt": "<string>"
}