Exception when calling CallbackApi->createCallback: [400] Error connecting to the API (https://smsgateway.me/api/v4/callback)

[hfrance]

[27-Jun-2020 15:22:44 UTC] PHP Fatal error: Uncaught SMSGatewayMe\Client\ApiException: [403] Error connecting to the API (https://smsgateway.me/api/v4/message/send) in /home/smsmarketing/public_html/api/client-php/lib/ApiClient.php:247
Stack trace:
#0 /home/smsmarketing/public_html/api/client-php/lib/Api/MessageApi.php(525): SMSGatewayMe\Client\ApiClient->callApi('/message/send', 'POST', Array, '[{"phone_number...', Array, '\SMSGatewayMe\C...')
#1 /home/smsmarketing/public_html/api/client-php/lib/Api/MessageApi.php(459): SMSGatewayMe\Client\Api\MessageApi->sendMessagesWithHttpInfo(Array)
#2 /home/smsmarketing/public_html/api/client-php/test.php(23): SMSGatewayMe\Client\Api\MessageApi->sendMessages(Array)
#3 {main}
thrown in /home/smsmarketing/public_html/api/client-php/lib/ApiClient.php on line 247

require 'vendor/autoload.php';

use SMSGatewayMe\Client\ApiClient;
use SMSGatewayMe\Client\Configuration;
use SMSGatewayMe\Client\Api\MessageApi;
use SMSGatewayMe\Client\Model\SendMessageRequest;

// Configure API key authorization: Authorization
SMSGatewayMe\Client\Configuration::getDefaultConfiguration()->setApiKey('Authorization', 'AAAAAAAAAAAPPPPPIIII');
// Uncomment below to setup prefix (e.g. BEARER) for API key, if needed
// SMSGatewayMe\Client\Configuration::getDefaultConfiguration()->setApiKeyPrefix('Authorization', 'BEARER');

$api_instance = new SMSGatewayMe\Client\Api\CallbackApi();
$callback = new \SMSGatewayMe\Client\Model\CreateCallbackRequest(); // \SMSGatewayMe\Client\Model\CreateCallbackRequest | callback to create

try {
$result = $api_instance->createCallback($callback);
print_r($result);
} catch (Exception $e) {
echo 'Exception when calling CallbackApi->createCallback: ', $e->getMessage(), "\n";
}

any idea ?