Im using Maya 2022.3 and mGear 4.0.7.
I have created a rig for EPIC Mannequin character via Guide Template Samples/EPIC Mannequin (Z-Up).
Everything looks fine, but when I try to connect it to Human IK (Like here: https://www.youtube.com/watch?v=_klvPZiemMA&t=44s
The Characterization works, but the control rig doesn’t. The Reference rig from Human IK appears really small and facing Y-Up.
I’m not very familiar with the Epic guides yet. But:
What is your Maya up-space set to? There may be a difference between Z-up in the guides, and Z-up in the Maya settings. Maybe you are supposed to keep Maya in Y-up? Maybe HIK can’t deal with Maya Z-up. (I don’t know. Hopefully someone who knows answers that.)
In all of my Unreal projects, I still use Y-up in Maya. But I haven’t used the Epic guides in production yet.
For the scale: In Maya, have you changed your Working Units Linear away from centimeters? If so, many things will not work. I highly recommend keeping your units set to “centimeter”. Many internal tools and commands in Maya rely on centimeters, and simply won’t work in another setting.