This is the answer I gave to another User with a similar question: https://community.amd.com/thread/244700 .
The last User and last replies in the thread has the same issue as you do concerning Amazon.
You need to contact Amazon directly and find out about how to get the coupon codes from them to redeem at AMD Rewards site. I provided the 1-800 Amazon Customer Service number on the last reply on the thread.
If you buy through Amazon/Newegg, make sure the actual supplier is one of the registered participants (coupon code will be supplied by them). If not covered by Am./New.