Ingest pipeline for nested type

I am trying to use Ingest pipeline for nested object and I am getting error.

        "type" : "ingest_processor_exception",
        "reason" : "java.lang.IllegalArgumentException: field [content] not present as part of path [content]",

This is my Index which has nested type..

    {
    "settings": {
    "index": {
    "analysis": {
    "analyzer": {
    "windows_path_hierarchy_analyzer": {
    "type": "custom",
    "tokenizer": "windows_path_hierarchy_tokenizer"
    }
    },
    "tokenizer": {
    "windows_path_hierarchy_tokenizer": {
    "type": "path_hierarchy",
    "delimiter": "\"
    }
    }
    },
    "number_of_shards": "1",
    "number_of_replicas": "1"
    }
    },
    "mappings": {
    "_doc": {
    "properties": {
    "casePartList": {
    "type": "nested"
    },
    "isRead": {
    "type": "boolean"
    },
    "CreationDate": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "userId": {
    "type": "keyword"
    },
    "titleKey": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "regimeNumber": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "documentList": {
    "type": "nested",
    "properties": {
    "path": {
    "analyzer": "windows_path_hierarchy_analyzer",
    "type": "text"
    },
    "attachment": {
    "properties": {
    "date": {
    "type": "date"
    },
    "indexed_chars": {
    "type": "long"
    },
    "content_type": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "keywords": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "author": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "containsMetadata": {
    "type": "boolean"
    },
    "name": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "language": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "title": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "content": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "content_length": {
    "type": "long"
    },
    "detect_language": {
    "type": "boolean"
    }
    }
    },
    "id": {
    "type": "integer"
    },
    "documentTitle": {
    "type": "keyword"
    },
    "incidentId": {
    "type": "integer"
    },
    "content": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    }
    }
    },
    "caseId": {
    "type": "integer"
    },
    "regimeName": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "caseName": {
    "type": "keyword"
    },
    "folderName": {
    "type": "text",
    "fields": {
    "keyword": {
    "ignore_above": 256.0,
    "type": "keyword"
    }
    }
    },
    "iD": {
    "type": "integer"
    },
    "incidentId": {
    "type": "integer"
    }
    }
    }
    }
    }

my ingest pipeline is

{"description":"Document attachment pipeline","processors":[{"attachment":{"field":"content","target_field":"attachment"}},{"remove":{"field":["content"]}}]}

Actual C# Code using NEST:
var IngestPipeline = _esProvider.Client.Ingest.PutPipeline("attachments", p => p
.Description("Document attachment pipeline")

                        .Processors(pr => pr
                       
                        .Attachment<Document>(a => a
                           
                            .Field(f => f.Content)
                            
                            .TargetField(f => f.Attachment)
                           
                          )
                               .Remove<Document>(r => r
                  .Field(f => f.Field(cx => cx.Content))
              )
                        )
                        );


        } 

Index is getting created but when i try to create document it gives below error

"type" : "ingest_processor_exception",
"reason" : "java.lang.IllegalArgumentException: field [content] not present as part of path [content]",

I think my ingest pipeline is not properly mapped with Document type which is nested type of Incident.

I am new to elastic search. Can you please guide me for this issue?