Sorry. This should be 

$parameters = arrary('createtoken' => $createAccountToken);

I then see

{"error":{"code":"createcreatemissingparam","info":"At least one of the parameters createcontinue, createreturnurl is required","*":"See https://myserver/w/api.php for API usage"}}

I will continue to work to understand the details for how to invoke the createaccount action.

Thanks,

Scott K