ELASTICSEARCH - Aggregations not working on string field - kibana

Question

Elastic search extraction query is returning expected results in hints section of output but aggregation on field returning empty response
output without aggregation
{
"_shards": {
"total": 45,
"failed": 0,
"successful": 45,
"skipped": 0
},
"hits": {
"hits": [
{
"_index": "logstash-wander-2022.08.17",
"_type": "fluentd",
"_source": {
"outboundResponseStatus": "SERVICE_UNAVAILABLE"
},
"_id": "Y2NlNjkzZmEtNjZlMi00NWY4LTllNWUtOWZmNWRhMjRkMzA3",
"sort": [
1660695790244
],
"_score": null
},
{
"_index": "logstash-wander-2022.08.17",
"_type": "fluentd",
"_source": {
"outboundResponseStatus": "CONFLICT"
},
"_id": "OWNmZTFiOWEtYWQ2Mi00OGViLWFmY2EtMGQ4ZDg1NzRiYWNk",
"sort": [
1660695781810
],
"_score": null
}
],
"total": 25,
"max_score": null
},
"took": 506,
"timed_out": false
}
But adding below aggregation along with query returning empty response
"aggregations": {
"outboundResponseStatus": {
"significant_terms": {
"field": "outboundResponseStatus",
"keyed": true
}
}
}
Below is the query
{
"size": 500,
"query": {
"bool": {
"must": [
{
"query_string": {
"query": "search string",
"default_field": "*",
"fields": [],
"type": "best_fields",
"default_operator": "or",
"max_determinized_states": 10000,
"enable_position_increments": true,
"fuzziness": "AUTO",
"fuzzy_prefix_length": 0,
"fuzzy_max_expansions": 50,
"phrase_slop": 0,
"analyze_wildcard": true,
"escape": false,
"auto_generate_synonyms_phrase_query": true,
"fuzzy_transpositions": true,
"boost": 1
}
},
{
"match_phrase": {
"message": {
"query": "search string",
"slop": 0,
"zero_terms_query": "NONE",
"boost": 1
}
}
},
{
"range": {
"#timestamp": {
"from": "now-10m",
"to": "now",
"include_lower": true,
"include_upper": true,
"format": "epoch_millis",
"boost": 1
}
}
}
],
"adjust_pure_negative": true,
"boost": 1
}
},
"version": true,
"_source": {
"includes": [
"outboundResponseStatus",
"outboundUri",
"message"
],
"excludes": []
},
"stored_fields": "*",
"script_fields": {},
"sort": [
{
"#timestamp": {
"order": "desc",
"unmapped_type": "boolean"
}
}
]
}
How to get aggregations based on field in hints results?