You're not the only one. Trade in discount was not working either. It sucks! It happens every year. Samsung should fix it the issue prior to the preorder event.
Just try again at a later time. A lot of people are trying to preorder now, Every year when a new device comes out this happens. You will all live and you will all get one eventually if you want it...
After changing my payment method multiple times, my order finally went through with my pre-order discount, first responder discount, etc. What a headache, but glad it finally went through!
