Can you confirm whether you have supported backplane and cabling on the server for NVMe. Only X10 backplane support NVMe drives. You can refer below links for supported backplane and cabling details for NVMe

https://www.dell.com/support/manuals/en-us/poweredge-r640/per640_ism_pub/backplane-details?guid=guid-b3535477-163e-4e58-91b2-978f00c263cd&lang=en-us

https://www.dell.com/support/manuals/en-us/poweredge-r640/per640_ism_pub/cable-routing?guid=guid-97280a84-9e95-4a04-901f-400c88c14645&lang=en-us

Can you also share where exactly you are looking for NVMe drive details. It will be visible under software raid controller S140. You can also check in iDRAC to see whether NVMe drives are shown under backplane

Hello,

There are a few things I would check. Can you check if the backplane of the server if it supports NVMe drives. If you're unsure, you may need to check what is the DPN# of the backplane, we can confirm if it does support. Reference: https://www.dell.com/support/manuals/en-us/poweredge-r640/per640_ism_pub/backplane-details?guid=guid-b3535477-163e-4e58-91b2-978f00c263cd&lang=en-us

Next would be, checking if the iDRAC, BIOS and RAID Controller firmware is up to date. 

By meaning that the server does not detect the NVMe drive, is it not listed in the RAID controller PD Management?