WHMCS 8.1 Issue with API Request getPackageTable

Error: Class 'ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\HttpTransportException' not found in /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-api-client/src/HttpClient/Plugin/ExceptionThrower.php:43
Stack trace:
#0 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/httplug/src/Promise/HttpFulfilledPromise.php(31): ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\ExceptionThrower->ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\{closure}()
#1 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-api-client/src/HttpClient/Plugin/ExceptionThrower.php(44): Http\Client\Promise\HttpFulfilledPromise->then()
#2 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/Plugin/VersionBridgePlugin.php(22): ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\ExceptionThrower->doHandleRequest()
#3 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginChain.php(48): ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\ExceptionThrower->handleRequest()
#4 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/Plugin/HeaderDefaultsPlugin.php(44): Http\Client\Common\PluginChain->Http\Client\Common\{closure}()
#5 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginChain.php(48): Http\Client\Common\Plugin\HeaderDefaultsPlugin->handleRequest()
#6 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/Plugin/RedirectPlugin.php(147): Http\Client\Common\PluginChain->Http\Client\Common\{closure}()
#7 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginChain.php(48): Http\Client\Common\Plugin\RedirectPlugin->handleRequest()
#8 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-api-client/src/HttpClient/Plugin/PathPrepend.php(34): Http\Client\Common\PluginChain->Http\Client\Common\{closure}()
#9 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/Plugin/VersionBridgePlugin.php(22): ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\PathPrepend->doHandleRequest()
#10 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginChain.php(48): ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\PathPrepend->handleRequest()
#11 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-api-client/src/HttpClient/Plugin/ApiVersion.php(38): Http\Client\Common\PluginChain->Http\Client\Common\{closure}()
#12 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/Plugin/VersionBridgePlugin.php(22): ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\ApiVersion->doHandleRequest()
#13 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginChain.php(48): ISPServerfarm\APIClients\ReleaseSuite\HttpClient\Plugin\ApiVersion->handleRequest()
#14 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/Plugin/AddHostPlugin.php(66): Http\Client\Common\PluginChain->Http\Client\Common\{closure}()
#15 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginChain.php(48): Http\Client\Common\Plugin\AddHostPlugin->handleRequest()
#16 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginChain.php(63): Http\Client\Common\PluginChain->Http\Client\Common\{closure}()
#17 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/PluginClient.php(90): Http\Client\Common\PluginChain->__invoke()
#18 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/HttpMethodsClient.php(148): Http\Client\Common\PluginClient->sendRequest()
#19 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/HttpMethodsClient.php(108): Http\Client\Common\HttpMethodsClient->sendRequest()
#20 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/php-http/client-common/src/HttpMethodsClient.php(55): Http\Client\Common\HttpMethodsClient->send()
#21 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-api-client/src/Api/AbstractApi.php(35): Http\Client\Common\HttpMethodsClient->get()
#22 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-api-client/src/Api/Client.php(15): ISPServerfarm\APIClients\ReleaseSuite\Api\AbstractApi->get()
#23 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-updater/src/Updater.php(714): ISPServerfarm\APIClients\ReleaseSuite\Api\Client->products()
#24 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-updater/src/Admin/DataController.php(142): ISPServerfarm\Solutions\Updater\Updater::getCustomerSuites()
#25 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-updater/src/Admin/AdminDispatcher.php(49): ISPServerfarm\Module\Addon\Updater\Admin\DataController->getPackageTable()
#26 /home/kundencenter/webapps/whmcs-kundencenter/public/modules/addons/ispserverfarm_updater/vendor/ispserverfarm/ispserverfarm-updater/base/ispserverfarm_updater.php(132): ISPServerfarm\Module\Addon\Updater\Admin\AdminDispatcher->dispatch()
#27 /home/kundencenter/webapps/whmcs-kundencenter/public/ispadmins/addonmodules.php(0): ispserverfarm_updater_output()
#28 {main}