Unable to retrieve countries, providers or devices tag stats from the Mailgun API

I am using the mailgun-php library (3.0).

In the example below I am able to retrieve regular stats but the providers list is empty.

var_dump: https://pastebin.com/HAt1JRPy

$mgClient = Mailgun::create('key-xxxxxxxxxxxxxxxxxxxxxxxxxxxxx');

$stats = $mgClient->tags()->stats($this->mgDomain, 'nbxxx_1125', array(
    "event" => ["accepted","delivered"],
    "resolution" => "month",
    "duration" => "1m"
));

$providers = $mgClient->tags()->providers($this->mgDomain, 'nbxxx_1125');

var_dump($providers);
var_dump($stats);
die();

Any clue?

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