Calling listTabs via the EnvelopesApi in docusign/esign-client threw a fatal "Class 'Number' not found" from ObjectSerializer.php. During deserialization the SDK passed the bare class name 'Number' to the deserializer instead of the namespaced \DocuSign\eSign\Model\Number, so PHP could not resolve it. The report came from a Laravel 5.x app using docusign/esign-client ^3.0, and several other users reproduced it.