Computer doesn't recognise installed Flexio V2 upgrade module

[rappel]

Trying to install an

HP Flex IO V2 10Gbase Network Adapter T Module 56Q71AA for 1L PCs - 56Q71AA-BD

in an

HP Elitedesk 805 G6 Desktop. 21L41E#ABU

They are sold in the UK by some retailers as compatible with this model. Others do not mention compatibility.

I've installed one that I bought a few days ago. Bit fiddly but the module had the correct connection physically and installed physically.

Within the OS (Proxmox) I can't see the hardware as recognised or indeed being identified anywhere in the boot logs.

I have a couple of confirmations that in other later models of the Elitedesk series this interface successfully runs in the same version of OS that I have, so it's a hardware compatibility/hardware issue (or I just haven't installed it correctly despite checking correct seating a few times)

Someone has suggested in another forum that these may not be supported but without any specific evidence or reason. 

I can't find any documentation on the HP site to confirm or deny this and before I start talking to and/or sending this back to the supplier it would be good to have a definitive answer.

Does anyone know if these two are supposed to be able to work together? or

better can anyone point me to an HP document that lists compatibility of FlexIO v2 modules and FlexIO V2 capable PCs.?

Also open to any info from someone who's tried this before? or anyone successfully running this combo were there any further steps such as obscure BIOS settings needed to get this to function?

Thanks in advance.