Nvidia Quadro P400 passthrough results in error

[A Former User]

I am currently trying to Passthrough my PNY Nvidia Quadro P400 to my Plex VM. Everything on the XCP-NG side is setup correctly and I already assigned to GPU to the VM. I used this guide for the configuration of the passthrough on the XCP-NG host: https://xcp-ng.org/docs/compute.html#pci-passthrough

Although the VM sees the GPU, I still needed to install the drivers for the P400 on the Plex VM. So I did. I installed the driver and then tried this command: nvidia-smi which unfortunately resulted into this error

[root@plex ~]# nvidia-smi
Unable to determine the device handle for GPU 0000:00:06.0: Unknown Error

Did anyone have a similar kind of problem? If so how did you resolve it?
On Proxmox I would just go to the VMID.conf and edit some things there, but on XCP-NG I cannot find anything about this issue related to the GPU passthrough.

[TheFrisianClause]

I am just curious in why this will not work on XCP-NG but will work on Proxmox when installing the drivers on the VM...