curl --request POST \
  --url https://api.headlesscommerce.io/v1/admin/returns/{id}/complete \
  --header 'Authorization: Bearer <token>'

{
  "id": "<string>",
  "order_id": "<string>",
  "customer_id": "<string>",
  "return_type": "refund",
  "status": "requested",
  "reason": "<string>",
  "reason_category": "defective",
  "customer_notes": "<string>",
  "admin_notes": "<string>",
  "lines": [
    {
      "id": "<string>",
      "order_line_id": "<string>",
      "quantity": 123,
      "reason": "<string>",
      "condition": "<string>",
      "exchange_variant_id": "<string>"
    }
  ],
  "refund": {
    "id": "<string>",
    "order_id": "<string>",
    "amount": {
      "amount": 123,
      "currency": "<string>"
    },
    "reason": "<string>",
    "restock": true,
    "status": "pending",
    "lines": [
      {
        "order_line_id": "<string>",
        "quantity": 123
      }
    ],
    "created_at": "2023-11-07T05:31:56Z"
  },
  "created_at": "2023-11-07T05:31:56Z",
  "updated_at": "2023-11-07T05:31:56Z"
}