InsertRecord for custom module where a Lead is referenced

InsertRecord for custom module where a Lead is referenced

While inserting a record in a custom module, records get inserted, all other fields are updated with provided data in the request but referenced 'Lead Id' is not being populated. May I know what's wrong going with this request?  Here is the insert request:

  1.  $url = "https://crm.zoho.com/crm/private/xml/CustomModule1/insertRecords";
                            $param= "authtoken=".$token."&scope=crmapi&xmlData=
                            <MailStamps>
                            <row no=\"1\">
                            <FL val=\"Lead Id\">$leadId</FL>
                            <FL val=\"field1\">$field1Value</FL>
                            <FL val=\"field2\">$field2Value</FL>
                            </row>
                            </MailStamps>
                            ";