Scripting Query for returning cases where array size is larger than X

I want to make a query that counts how many elements there are in the field that is a array of jsons objects.

When I run:

{script: { script: "doc['field_name'].values.length() > 0"}}

I get:

"No field found for [field_name] in mapping with types "

I have set mapping for field_name as nested, but still I am getting the same error

I have tried multiple variations for the query but none of them worked:

"script" : "params['_source']['field_name'].length() > 1"
"script" : "params['_source']['field_name'].size() > 1"
"script" : "params['_source']['field_name'].values.size() > 1"
"script" : "params['_source']['field_name.keyword'].values.size() > 1"
"script" : {"source": "doc['ctx._source.field_name'].lenght() > 0" }}
and other variations.

What am I doing wrong ?

any more information I could provide ?

yes, a fully reproducible example, including index creation, mapping, document indexing and the query. Also, the Elasticsearch version you are using.