The constructor of TransactionalSMSApi should be fixed the same way you fixed TransactionalEmailApi to be compatible with php 8.4.
public function __construct(
?ClientInterface $client = null,
?Configuration $config = null,
?HeaderSelector $selector = null
) {
$this->client = $client ?: new Client();
$this->config = $config ?: new Configuration();
$this->headerSelector = $selector ?: new HeaderSelector();
}