Example of how to use oneOf on a required property instead of on the object body.

gift.json

{
  "type": "array",
  "items": {

        "type": "object",
        "description": "A product or piece of merchandise purchased with, points.",
        "properties": {
          "giftID": {
            "type": "string",
            "description": "A unique ID for differentiating gift objects"
          },
          "inventoryCount": {
            "type": "integer",
            "description": "The number of gifts currently available. This property allows the gift's availability to differ from its item or merchandise. Specify -1 for unknown."
          },
          "unitPoints": {
            "type": "number",
            "description": "The points required to purchase a single unit of this gift."
          },
          "item": {
            "properties": {
                "itemID": {"type": "string"},
                "inventoryCount":{ "type":"number"}
            },
            "required": ["itemID", "inventoryCount"]
          },
          "merchandise": {
            "type": "object",
              "properties": {
                "merchID": {
                  "type": "string"
                }
              },
              "required": ["merchID"]
          }
        },
        "required": [
          "giftID",
          "inventoryCount",
          "unitPoints"
        ],
        "oneOf": [{"required": ["item"]}, {"required": ["merchandise"]}]
      
  }
}

working example of above on TV4