fix: 카카오톡 bulk send 오류 fix

mens-api/src/main/java/kr/xit/ens/kakao/v2/service/KkotalkEltrcDocService.java

@@ -237,10 +237,11 @@ public class KkotalkEltrcDocService extends AbstractService implements
         if(!errors.isEmpty()){
             throw BizRuntimeException.create(errors.toString());
         }
+        String param = "{\"envelopes\":" + JsonUtils.toJson(envelopes) + "}";
         return webClient.exchangeKkotalk(
             HOST + API_SEND[0].replace("{PRODUCT_CODE}", reqDTO.getProductCode()),
             HttpMethod.valueOf(API_BULKSEND[1]),
-            JsonUtils.toJson(envelopes),
+            param,
             KkotalkDTO.BulkSendResponse.class,
             getRlaybsnmInfo(reqDTO));
     }