undefined function net\authorize\api\contract\v1\ is_object()

[packytagliaferro]

I am using the sample code from the PHP SDK and the package throws an error of

Call to undefined function net\authorize\api\contract\v1\ is_object().

It looks like its coming from this call:

$response = $controller->executeWithApiResponse(\net\authorize\api\constants\ANetEnvironment::SANDBOX);

That in turns calls this:

vendor/authorizenet/authorizenet/lib/net/authorize/api/contract/v1/CreateTransactionResponse.php:72

I am running PHP 7.4 but why is this being thrown?