Search_phase_execution_error with script_Score n cosine similarity ES 7.15.2

[Nikkie]

Greetings! I had started with my Elasticsearch journey with 7.10.1 and could successfully run script_score queries with cosine_similarity earlier. But now when I am using 7.15 I get stuck with this error "Elasticsearch.exceptions.RequestError: RequestError(400, 'search_phase_execution_exception', 'runtime error')" even for a trial dataset of 20 records. I am stuck on this for about a week, tried installing and working with earlier versions of ES too. but still same error.
My index mapping:

  "mappings": {
          "properties": {
              "id":{"type":"long"},
              "prompt": {
                  "type": "text",
                  "analyzer": "standard",
                  "fields": {
                      "keyword": {"type": "keyword"},
                      "ngrams": {"type": "text", "analyzer": "ngram_analyzer"}
                  }
              },
            "cf": {
                "type": "keyword" },
            "entities": {
                "type": "keyword" },
            "keywords": {
                "type": "keyword" },
            "promptVec":{
                "type": "dense_vector","dims":512
            }
          }

My Query:

esq = {"query":{ 
 "script_score":{
            "query":{"match_all":{}},
            "script":{
                "source":"cosineSimilarity(params.qv, doc['promptVec'])+1.0",
                "params":{"qv":query_vector}
            }
        } }
    } ```
ERROR: raise HTTP_EXCEPTIONS.get(status_code, TransportError)(

elasticsearch.exceptions.RequestError: RequestError(400, 'parsing_exception', 'unknown query [query]')

I also tried (as debug step) to reduce no of dims to 5 and indexing only 20 records, but the same error persists. Any help is greatly appreciated