Is it possible to take a picture of the manual and upload it here ? And also show us your footpeg area to see what they mean by that.
In the past , i basically used universal pannier kits (was cheaper) but were hard shells which I needed and also got a universal rack kit that mounts to the sides of the grab rails along the rear pillion area. I just had to get creative and swear a lot to make things fit! This was on a bigger older GV (carb ) , personally I have not fitted one to a GV125-S, however Hyosung did not change any structural parts for the footrests since 2018-2025
The major change in 2024/2025 is their new model called GV-125X (X) , totally looks different. S-models will remain S-models without much change visually to be fair
The worst is that you could end up getting a metal plate fabricated to get around fitting the boxes or return it but i would also email or contact Shad themselves.
They are an OK company (quality wise), personally I use their Click-Lock tank bag systems, but as for customer support I can’t comment as i never had to bother them about any issues i had personally with their products.
Keep us posted!