Create Extensions that have no real Extension Number associated?

Create Extensions that have no real Extension Number associated?

I need to create about 10K user extension entries to be used in the Corporate Directory but these users have external NON-RingCentral phone numbers.

How do I create these extensions? When trying to create one using the "Try It Now" API testing I get the following error:

"Invalid user type [VirtualUser] for current account service plan."