vuongxuongminh / yii2-gateway-clients

examples/example.php

<?php

use vxm\examples\gatewayclients\Gateway;

$responseData = (new Gateway([
    'client' => [
        'username' => 'vxm'
    ]
]))->request('refund', ['amount' => 1000]);

if ($responseData->isOk) {

Accessing isOk on the interface GatewayClients\DataInterface suggest that you code against a concrete implementation. How about adding an instanceof check?

    print_r($responseData->get());
}