Error when testing Stripe payment gateway

Howdy!

First things first: I really love all the plugins and functionality you folks at wpmudev have built and offered; Keep up the good work!

Now, to my problem: I'm testing the Stripe payment gateway for Pro Sites (thanks for including them, BTW!). I set everything to testing mode, got the card info form on my page, filled it in with a testing card number, etc., but when I clicked "subscribe," I got a red error box that said "Received unknown parameter: trial_period_days."

What can I do to remove this error?

Thanks!

-aj