I am using HTTP server and this is my message via the firebase server
$fcm = array
'to' => $stored_token,
'priority' => 'high',
'time_to_live' => 0,
'data' => array
'msg' => 0
Table 5 in the documentation for FCM HTTP Server Protocol indicates that
failure count in the response is the
Number of messages that could not be processed
The reasons for processing failure are listed in Table 9. All the reasons are related to a problem with the request parameters, such as invalid format, value missing, etc. Your request is valid, so is counted as a success.
In your post, you say "This behavior is against as stated in the documents". Please update your post to include a link to the document that state a delivery failure should be counted as a processing failure.