AMD's 3 year Warranty becomes effective as soon as the Retailer/Vendor's Warranty expires. In this case, Amazon's Return policy.
But you mentioned that you had the processor working for about 6 months which rules out Amazon Return policy. Unless you purchased an Amazon 3 or 4 year Protection plan when you purchased the processor from Amazon.
So you need to go through AMD Warranty to get your processor RMAed and replaced.
Could also be a AMD Server problem, In which case I would wait a day and try again.
Did you follow all the instructions on how to fill out the Online Warranty Service Request: https://www.amd.com/en/support/kb/warranty-information/rma-form
The information is on the Retail box and tattooed on the CPU surface.