If you are testing the 2-step order form tied to a SaaS Mode plan and the sale is not generating a new sub-account, the issue is likely that your sub-account is using "Test Mode" API keys from Stripe.
Note: For SaaS Mode to work:
1) The sub-account where you'll be building the sales page with a 2-step order form tied to your SaaS Mode plans must be integrated with the same Stripe account that the agency account is integrated with
2) Both the sub-account and the agency account need to be integrated with live Stripe API keys. Use a real credit card when testing and just refund the amount in Stripe