Push notifications android 1st, then iOS

i need help. i have the server side PHP sample code, just need to get things right to get it to work. currently i am getting this error from the server sending the msg, Error 401: Invalid (legacy) Server-key delivered or Sender is not authorized to perform request. can add you to firebase to see the information can give you my token to test. PHP sample code: $notification = array ( 'title' => $receiverName. ': A new message for you', 'body' => $message, 'sound' => 'default' ); $data = array ( 'message' => $message, 'click_action' => "PUSH_INTENT" ); $fields = array ( 'registration_ids' => $registrationIds, 'notification' => $notification, 'data' => $data, 'priority' => 'normal' ); $headers = array ( 'Authorization: key='.API_ACCESS_KEY, 'Content-Type: application/json' ); $ch = curl_init(); curl_setopt( $ch,CURLOPT_URL, '[login to view URL]' ); curl_setopt( $ch,CURLOPT_POST, true ); curl_setopt( $ch,CURLOPT_HTTPHEADER, $headers ); curl_setopt( $ch,CURLOPT_RETURNTRANSFER, false); //true orig ); returns err info if false curl_setopt( $ch,CURLOPT_SSL_VERIFYPEER, false ); curl_setopt( $ch,CURLOPT_POSTFIELDS, json_encode( $fields ) ); $result = curl_exec($ch ); curl_close( $ch );