Customers unable to complete pre-orders with $0 deposit

From the webstore, we have a couple of customers unable to complete the checkout when trying to set up a preorder that does not require a deposit. Please investigate.

Thanks!

Hi Andy,

Do you know if they were trying to use Paypal?

I'll need to get more details. I believe they had a checkout total of $0 - do they still need to enter a payment method with that?