So, basically, there's a Goku Koikatsu Card that doesn't work for me. I've tried to download all the mods using KKManager but, no use.

The card is this https://illusioncards.booru.org/index.php?page=post&s=view&id=72508.

What happens to it is, that the hair is not there, and the arms and upper chest are also not there. So,

Does anyone know how to fix this?

I tested it and it works fine for me. Do you have the latest version of the HF patch and koikatsu manager. And the latst better repack? that is all I can think of that could be cousing your problems with this card.

I tried detecting the mods with "koikoi.happy.nu/mod_detector", but it doesn't detect it as a card. I wonder why? Maybe it has something to do with this problem, compatibility problems or something.
Anyways, i had a lot of similar problems with newer cards, so i updated to the latest BetterRepack, and now all cards seem to work, so that is a possible fix.