Find exact error code or error message in responce

[aruljames93]

Hi,
In FCM push notification i'm getting numberSuccess() or numberFailure() BOOLEAN values (0,1). But i need to get exact error exception from return response. Is there any way to get exact error message from this FCM Package ????

$downstreamResponse->numberSuccess();
$downstreamResponse->numberFailure();
$downstreamResponse->numberModification();
$downstreamResponse->tokensToDelete();
$downstreamResponse->tokensToModify();
$downstreamResponse->tokensToRetry();
$downstreamResponse->tokensWithError();