public class Flr_Insert_Records {
    
    Public static void Insert_Records(){
        /* Http http = new Http();
HttpRequest request = new HttpRequest();
request.setEndpoint('http://fpdatamap.salesforceoutsourcing.in/api/FPData');
request.setMethod('POST');
request.setHeader('Content-Type','application/json');
//request.setHeader('Content-Type','multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW');
//request.setHeader('Authorization','Bearer '+ AuthorizationToken);*/
        
        List<Opportunity_Prod_Batch_Record__c> oppbatch=[select Edition_Name__c,Opportunity_Id__c,Opportunity_Name__c,Opportunity_Stage__c,Stand_No__c,Banner_name__c
                                                         from Opportunity_Prod_Batch_Record__c  ];
        system.debug('oppbatch List query.. '+oppbatch);
        // system.debug('Query after serialization '+json.serialize(oppbatch));
        /*OppWrapper oppwrappervar=new OppWrapper(oppbatch[0].Edition_Name__c,oppbatch[0].Opportunity_Id__c,oppbatch[0].Opportunity_Name__c,
                                                oppbatch[0].Opportunity_Stage__c,oppbatch[0].Stand_No__c,oppbatch[0].Banner_name__c);
        string jsonbody=Json.serialize(oppwrappervar);*/
        // Right code 
List<OppWrapper> oppWrapperVarList = new List<OppWrapper>();
for(Opportunity_Prod_Batch_Record__c oppbtch : oppbatch) {
   OppWrapper oppwrappervar=new OppWrapper(oppbtch.Edition_Name__c,oppbtch.Opportunity_Id__c,oppbtch.Opportunity_Name__c,oppbtch.Opportunity_Stage__c,oppbtch.Stand_No__c,oppbtch.Banner_name__c);
oppWrapperVarList.add(oppwrappervar);
}
 string jsonbody=Json.serialize(oppWrapperVarList);
        system.debug('Json body---->'+jsonbody);
        
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint('http://fpdatamap.salesforceoutsourcing.in/api/FPDatas');
        request.setMethod('POST');
        request.setHeader('Content-Type','application/json');
        //request.setHeader('Content-Type','multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW');
        //request.setHeader('Authorization','Bearer '+ AuthorizationToken);
//request.setBody('[{ "RecordId": "456","RecordName": "moosa traders pvt ltd / The Big 5 Construct Egypt 2018 /  / 093061123", "EventName": "a2JD0000001ns6uMAA U", "RecordStage": "Test Stage Amjad","BannerName": "Test Banner Amjad","StandNo": "Test Stand Amjad"}]');
        request.setBody(jsonbody);
        
       HttpResponse response = http.send(request);
        system.debug('Response body '+ response.getBody());
if (response.getStatusCode() != 201) {
    System.debug('The status code returned was not expected: ' +
        response.getStatusCode() + ' ' + response.getStatus());
} else {
    System.debug(response.getBody());
}
        
        
    }
    
    public class OppWrapper
    {
        public String EventName {get;set;}
        public String RecordId {get;set;}
        public String RecordName {get;set;}
        public String RecordStage {get;set;}
        public String StandNo {get;set;}
         public String BannerName {get;set;}
        public OppWrapper(String EventName,String RecordId,String RecordName,String RecordStage,String StandNo,String BannerName)
        {
            this.EventName =EventName;
            this.RecordId =RecordId;
            this.RecordName =RecordName;
            this.RecordStage=RecordStage;
            this.StandNo=StandNo;
            this.BannerName=BannerName;
            
        }
    }
    
}

it is working fine just i need to do whnerver records existis then it will skeep that record and post remaning records how to achive that please help me..................