curl --request PUT \
  --url https://api.retrac.co/inventory/balances \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "itemId": "<string>",
  "locationId": "<string>",
  "onHandQty": 1,
  "note": "<string>"
}
'

{
  "id": "<string>",
  "itemId": "<string>",
  "locationId": "<string>",
  "onHandQty": 123,
  "item": {
    "id": "<string>",
    "sku": "<string>",
    "description": "<string>"
  },
  "location": {
    "id": "<string>",
    "name": "<string>"
  }
}