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--- a/README.md
+++ b/README.md
@@ -407,6 +407,7 @@ class App extends Component {
 Firebase android misses important feature of android notification like `group`, `priority` and etc. As a work around you can send data message (no `notification` payload at all) and this repo will build a local notification for you. If you pass `custom_notification` in the payload, the repo will treat the content as a local notification config and shows immediately.
 
 NOTE: By using this work around, you will have to send different types of payload for iOS and Android devices because custom_notification isn't supported on iOS
+NOTE2: `custom_notification` **cannot** be used together with `notification` attribute. use `data` only
 
 Example of payload that is sent to FCM server:
 ```