I just received this from HTC support :
"We are investigating on the backend why this is failing. In order to keep you from having to wait needlessly, what I would like to do is offer you this as a workaround to a missing discount code:
1. This would require that you place the preorder number without the discount.
2. You would provide me the order number which I would put on a list
2. When the orders for the Vive Pro 2 units ship to their new homes, we would revisit the list and go in and manually refund you $50
If you'd like me to set that up for you, please make your order and provide me with the order number. I will provide you with confirmation once that order number is on the list"
So I just placed my order and emailed them my order number. Just waiting for the confirmation.