Invoices with 100% off coupon don't process

I mentioned this in another comment, but decided it may need its own thread. We’re using Invoicing with GeoDirectory. When someone signs up a free listing or paid listing, everything works fine with our Stripe Payment Gateway. However, there are a handful of people we have given coupons for a free featured listing. When they put the coupon in it changes the invoice price to zero and they don’t have to put in a credit card, just as it should. But then when they hit “complete payment”, the button greys out and the page just sits there forever. It doesn’t freeze, the console doesn’t kick any errors, there is no visible sign anything goes wrong. It just stays the same and both the payment and the listing get stuck in “pending”.

Thanks!