CURL needs the Legacy server key, it seems

Author: EddyVerbruggen

docs/MESSAGING.md

@@ -165,8 +165,8 @@ Using the Firebase Console gives you most flexibility, but you can quickly and e
 curl -X POST --header "Authorization: key=SERVER_KEY" --Header "Content-Type: application/json" https://fcm.googleapis.com/fcm/send -d "{\"notification\":{\"title\": \"My title\", \"text\": \"My text\", \"badge\": \"1\", \"sound\": \"default\"}, \"data\":{\"foo\":\"bar\"}, \"priority\": \"High\", \"to\": \"DEVICE_TOKEN\"}"
 ```
 
-* SERVER_KEY: see below
-* DEVICE_TOKEN: the one you got in `addOnPushTokenReceivedCallback` or `init`'s `onPushTokenReceivedCallback`
+* SERVER_KEY: see the image below (make sure to use the 'Legacy' server key).
+* DEVICE_TOKEN: the one you got in `addOnPushTokenReceivedCallback` or `init`'s `onPushTokenReceivedCallback`.
 
 Examples: