In order to access the custom managed properties we have to add them under SharePoint -> SharePoint admin center -> Manage Search Schema
You simply add your new managed property and associate it with the crawled property.
Then your CSOM C# code should look like this:
KeywordQuery keywordQuery = new KeywordQuery(clientContext); keywordQuery.QueryText = "path:\"https://onebitchh.sharepoint.com/sites/ilm/lists/Retention Rules\" AND ContentType:Item"; keywordQuery.ClientType = "CSOM"; keywordQuery.SelectProperties.Add("CountryOWSCHCS"); keywordQuery.SelectProperties.Add("CountryLegalRetentionPeriodStatus"); keywordQuery.SelectProperties.Add("CCHDocClassOWSTEXT"); keywordQuery.SelectProperties.Add("CCHDocumentDescripOWSMTXT"); keywordQuery.SelectProperties.Add("ContentType"); keywordQuery.SelectProperties.Add("ContentTypeId"); keywordQuery.SelectProperties.Add("SPContentType"); SearchExecutor searchExecutor = new SearchExecutor(clientContext); ClientResult<ResultTableCollection> results = searchExecutor.ExecuteQuery(keywordQuery); clientContext.ExecuteQuery();
If the crawl is finished you should be able to see the results from your new managed property associated with site/list column: