Is this a USA Warranty or International Warranty Claim? Asking due to different Servers being used.
Which AMD Hardware are you trying to open a Warranty claim for? CPU or GPU?
Are you using a VPN to upload the file? if so, try disabling the VPN first and see if it uploads or not.
Otherwise follow @FunkZ suggestion to find out exactly what is going on.
You can open a AMD SUPPORT - WARRANTY Ticket to see if they can help you find a way to upload your .PDF file.
This is not AMD WARRANTY but AMD SUPPORT: https://www.amd.com/en/forms/contact-us/support.html