Mage2\Paypal\Payment\Paypal::setApiContext PHP Method

    public function setApiContext($clientId = null, $clientSecret = null, $requestId = null)
    {
        if (null === $clientId) {
            //$clientId  = config('paypal.api-client-d');
            $clientId = Configuration::getConfiguration('paypal_client_id');
        }
        if (null === $clientSecret) {
            //$clientSecret = config('paypal.api-client-secret');
            $clientSecret = Configuration::getConfiguration('paypal_client_secret');
        }
        $credentials = new OAuthTokenCredential($clientId, $clientSecret);
        $this->_apiContext = new ApiContext($credentials, $requestId);
        return $this;
    }