Pro Site - test payment not processing

I'm new to WPMUDEV. I created a test multisite system and installed Pro Sites. I setup a Stripe account and created a gateway with my test Publishable key and test Secret key. I created some levels with different prices. When I buy a plan, the Stripe API kicks in and I can use the test card number (as directed by Stripe) of 5555555555554444. When I click "Subscribe" it says processing for a few seconds and then it clears out the form and stays on that page. I was expecting it to create the site and go to a thank you page. Can you please help me troubleshoot this?