price_rule_id path parameter is the ID of the price rule that the discount code will belong to. This is required becausecurl --location --request POST 'https://demo.myshopify.com//admin/api//price_rules//discount_codes.json'{
    "discount_code": {
        "id": 1054381139,
        "price_rule_id": 507328175,
        "code": "SUMMERSALE10OFF",
        "usage_count": 0,
        "created_at": "2023-01-03T12:38:34-05:00",
        "updated_at": "2023-01-03T12:38:34-05:00"
    }
}