No post or power with secondary riser installed.

[sappireflames00]

I have a DL385 plus gen 10 server with 2 epyc 7502 and 1.25 TB of memory installed. everything functions normally except when I try to add a secondary riser. The unit gives a critical error with the red status light flashing. In this state the unit cannot power on. I'm fairly new to servers in general, so I just need to know if this is user error, or a faulty riser. P/N for the riser is, P14590-B21. Is there any configuration nessesary before installation?

I've tried the riser with 1 and both cpu's, different memory, and looked through ilo config to see if there was anything obvious, though I didn't have any luck. Any help would be much appriciated.