curl --request POST \
  --url 'https://api.stateset.com/api/v1/backorders/{id}/fulfill' \
  --header 'Authorization: Bearer YOUR_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
  "fulfilled_by": null,
  "notes": null,
  "quantity": "string",
  "source_id": null,
  "source_type": null
}'

{
  "backorder_number": "string",
  "created_at": "string",
  "customer_id": "string",
  "expected_date": null,
  "id": "string",
  "order_id": "string",
  "priority": "string",
  "promised_date": null,
  "quantity_fulfilled": "string",
  "quantity_ordered": "string",
  "quantity_remaining": "string",
  "sku": "string",
  "status": "string"
}