Animation retargeting broken orientation

Hi,

I’ve been trying to re-target some animations from an FPS arms only skeleton to a full humanoid skeleton. I was able to setup and re-target as per many guides on various sources, I have even studied the unreal documentation self to try and get my issue solved.

So my issue is that once I re-target the selected animation from one rig to the other it seems that the orientation of the arms is twisted 90 degrees downward and I am not sure how to get this fixed.

Source rig:

Target rig:

Desired animation (what it looks like):

And the resulted retarget animation into target rig:

Any ideas on what I am doing wrong will be much appreciated!