Checkout Gets Stuck

I do pictures for a great organization. Each person gets one free digital image. Like every other year, they are instructed to make sure to put the free image in their cart and check out. The problem is that if they are not buying anything else the checkout process gets stuck on the payment screen so they can't complete the order. I'm sure it's something I've done wrong, but I'm not sure what that would be. 

Thanks!

You had the Square payment option enabled, but it didn't have all the required credentials (no location ID) so it was creating an hidden error and making the place order button not show. I disabled Square and it is working now.

Thanks!! I knew it was something I did.