{
  "indices.flush_synced": {
    "documentation": "http://www.elastic.co/guide/en/elasticsearch/reference/master/indices-synced-flush.html",
    "stability": "stable",
    "methods": ["POST", "GET"],
    "url": {
      "paths": [
        "/_flush/synced",
        "/{index}/_flush/synced"
      ],
      "parts": {
        "index": {
          "type" : "list",
          "description" : "A comma-separated list of index names; use `_all` or empty string for all indices"
        }
      },
      "params": {
        "ignore_unavailable": {
          "type": "boolean",
          "description": "Whether specified concrete indices should be ignored when unavailable (missing or closed)"
        },
        "allow_no_indices": {
          "type": "boolean",
          "description": "Whether to ignore if a wildcard indices expression resolves into no concrete indices. (This includes `_all` string or when no indices have been specified)"
        },
        "expand_wildcards": {
          "type": "enum",
          "options": [
            "open",
            "closed",
            "none",
            "all"
          ],
          "default": "open",
          "description": "Whether to expand wildcard expression to concrete indices that are open, closed or both."
        }
      }
    },
    "body": null
  }
}

{
  "indices.flush_synced": {
    "documentation": "http://www.elastic.co/guide/en/elasticsearch/reference/master/indices-flush.html#indices-synced-flush",
    "stability": "stable",
    "methods": ["POST", "GET"],
    "url": {
      "paths": [
        "/_flush/synced",
        "/{index}/_flush/synced"
      ],
      "parts": {
        "index": {
          "type" : "list",
          "description" : "A comma-separated list of index names; use `_all` or empty string for all indices"
        }
      },
      "params": {
        "ignore_unavailable": {
          "type": "boolean",
          "description": "Whether specified concrete indices should be ignored when unavailable (missing or closed)"
        },
        "allow_no_indices": {
          "type": "boolean",
          "description": "Whether to ignore if a wildcard indices expression resolves into no concrete indices. (This includes `_all` string or when no indices have been specified)"
        },
        "expand_wildcards": {
          "type": "enum",
          "options": [
            "open",
            "closed",
            "none",
            "all"
          ],
          "default": "open",
          "description": "Whether to expand wildcard expression to concrete indices that are open, closed or both."
        }
      }
    },
    "body": null
  }
}

Correct link for synced index flush
[DOCS] Correct link for synced index flush
