Query N1QL FTS facets

Hi!

I created a FTS with city field as keyword:

But when I try to get info abouts facets, it doesn´t get facet info.

Docs schema:

[
  {
    "_class": "XXXX.SchoolDocument",
    "address": "C/VIRGEN DEL MAR",
    "address_number": 2,
    "city": "ALMERIA",
    "collective": "HIJAS CARIDAD ANDALUCIA",
    "email": "XXX@HOTMAIL.COM",
    "index": "XXX_es",
    "latitude": 36.83756,
    "longitude": -2.46483,
    "name": "NTRA. SRA. DEL MILAGRO",
    "province": "ALMERIA",
    "school_id": 439007,
    "telephone": 95000000,
    "zip_code": 4002
  },
  (...)

This is my query (N1QL):

select s.*
from `XXX-local` s
WHERE  SEARCH(s,
   {"query": {
       "must": {
                   "conjuncts": [
                        {"field":"_class", "match": "XXXX.SchoolDocument"},
                        {"field":"province", "wildcard": "*ALM*"}
                    ]
       }
    },
  	"facets": {
		"cities": {
			"size": 5000,
			"field": "city"
		}
	},
    "fields": ["*"],
    "sort": ["-_id"],
    "size": 100, "from": 0
  }
)
;

Result by query, same as document saved (no facets section):

[
  {
    "_class": "XXXX.SchoolDocument",
    "address": "C/VIRGEN DEL MAR",
    "address_number": 2,
    "city": "ALMERIA",
    "collective": "HIJAS CARIDAD ANDALUCIA",
    "email": "XXX@HOTMAIL.COM",
    "index": "XXX_es",
    "latitude": 36.83756,
    "longitude": -2.46483,
    "name": "NTRA. SRA. DEL MILAGRO",
    "province": "ALMERIA",
    "school_id": 439007,
    "telephone": 950000000,
    "zip_code": 4002
  },
  (...)

What am I doing wrong?

Thanks in advance.