I cannot check the warranty of my WD80PURZ s devices

I get an invalid serial number error when I try to check the warranty of my running disks on my Backup Unit. I know that my discs have a production date of 20 May 2017 and their warranties continue, but I keep getting the same error even though I have entered the serial numbers of the discs correctly. The model numbers of my discs are WD80PURZ. Many thanks in advance for your help