Where do the repetitions in the table come from?

Question

Google Apps Script

Hello.
I use this code

async function CitiesNovaPoshta2 () {
  const sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Города");
  let x = 0;
  var payload = {
    'apiKey': '********************************************',
    'modelName': 'Address',
    'calledMethod': 'getCities',
  }
  var options = {
    'method' : 'post',
    'headers': {
      'content-type': 'application/json',
    },
    'payload': JSON.stringify(payload),
  };
  while (x < 10) { 
    var result = await UrlFetchApp.fetch('https://api.novaposhta.ua/v2.0/json/', options);
    if (result) {break;}        
    x++
  }; 
  var dataCities =  JSON.parse(result.getContentText());
  //var orderList1 = JSON.stringify(dataCities, null, 2);
  //Logger.log(orderList1);
  const  lengthCities =  dataCities["data"].length;
  const array = [];
  //for (let i = 0; i < lengthCities; i=i+10) {
   for (let i = 0; i < 200; i=i+10) { 
    array[i] = []; // создаем подмассив
    for (let j= i; j<i+10; j++){
      let buffer = [];
      
      buffer.push(dataCities["data"][j]["Description"]);
      buffer.push(dataCities["data"][j]["DescriptionRu"]);
      buffer.push(dataCities["data"][j]["Ref"]);
      buffer.push(dataCities["data"][j]["Delivery1"]);
      buffer.push(dataCities["data"][j]["Delivery2"]);
      buffer.push(dataCities["data"][j]["Delivery3"]);
      buffer.push(dataCities["data"][j]["Delivery4"]);
      buffer.push(dataCities["data"][j]["Delivery5"]);
      buffer.push(dataCities["data"][j]["Delivery6"]);
      buffer.push(dataCities["data"][j]["Delivery7"]);
      buffer.push(dataCities["data"][j]["Area"]);
      buffer.push(dataCities["data"][j]["SettlementType"]);
      buffer.push(dataCities["data"][j]["IsBranch"]);
      buffer.push(dataCities["data"][j]["CityID"]);
      buffer.push(dataCities["data"][j]["SettlementTypeDescription"]);
      buffer.push(dataCities["data"][j]["SettlementTypeDescriptionRu"]);
      buffer.push(dataCities["data"][j]["SpecialCashCheck"]);
      buffer.push(dataCities["data"][j]["Postomat"]);
      buffer.push(dataCities["data"][j]["AreaDescription"]);
      buffer.push(dataCities["data"][j]["AreaDescriptionRu"]);
      buffer = buffer.map(x=>[x])
       array.push(buffer);
    }
   Logger.log(array);
   await sheet.getRange(sheet.getLastRow() + 1,1,array.length, array[0].length).setValues(array);
   // SpreadsheetApp.flush()
  }
}

There are a lot of duplicate cities in the Google spreadsheet. Although there are no repetitions in the original array. I suppose that it is necessary to number the creating arrays somehow and put them in the table in order. Can anyone help me how to do this correctly so that there are no repetitions?