diff --git a/README.md b/README.md
index c8ce334..2d6751a 100644
--- a/README.md
+++ b/README.md
@@ -526,7 +526,7 @@ Request body must has a notifications array. The following is a parameter table
 | data                    | string array | extensible partition                                                                              | -        |                                                               |
 | retry                   | int          | retry send notification if fail response from server. Value must be small than `max_retry` field. | -        |                                                               |
 | topic                   | string       | send messages to topics                                                                           |          |                                                               |
-| api_key                 | string       | Android api key                                                                                   | -        | only Android                                                  |
+| api_key                 | string       | api key for firebase cloud message                                                                                   | -        | only Android                                                  |
 | to                      | string       | The value must be a registration token, notification key, or topic.                               | -        | only Android                                                  |
 | collapse_key            | string       | a key for collapsing notifications                                                                | -        | only Android                                                  |
 | delay_while_idle        | bool         | a flag for device idling                                                                          | -        | only Android                                                  |