Help with RAM for HP ProLiant Microserver Gen 8

[gez737]

I purchased a HP PROLIANT MICROSERVER GEN 8 (Part Number of HP server: 718897-001)

It came with the default 2GB of RAM (1 x 2GB), however this is notsufficient and I would like to upgrade the RAM.
I had thought I had purchased the correct RAM to upgrade, but it does not recognise it. 
Can you please help and advise what RAM I require for it to detect and work correctly?

* Do I need matching RAM in each slot? or can I mix and match the RAM sizes?

The memory requirements for the server are attached

I have read that some types of RAM won't work in the server?

Thank you.

gez737