There are a few arguments in code examples that were missed:
Converting Property Names when Serializing and Deserializing

$json = $serializer->serialize($obj);
// {"org_name": "Acme Inc.", "org_address": "123 Main Street, Big City"}
$objCopy = $serializer->deserialize($json);

It should looks like:
$json = $serializer->serialize($obj, 'json');
// {"org_name": "Acme Inc.", "org_address": "123 Main Street, Big City"}
$objCopy = $serializer->deserialize($json, Company::class, 'json');