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. To find your Stripe API keys, please refer to this Stripe Help Article on locating API keys. Also, be sure to use a valid credit card when testing, which you can then refund within Stripe when testing is complete.