Jattier

I was able to download it. I'm using Chrome. There is an error on the site about mixed content. By opening the Developer Tools and the Console, I can see the error message and a link is there for the https address for the unity package. Click it and the file will download. Mixed Content: The site at 'https://arteria3d.invisionzone.com/' was loaded over a secure connection, but the file at 'https://arteria-gaming.net/Spartan_UMA_Arteria3d_blahblahblahblah/Spartan_Warrior_UMA_Arteria3d.unitypackage' was redirected through an insecure connection. This file should be served over HTTPS. See https://blog.chromium.org/2020/02/protecting-users-from-insecure.html for more details.

I'm using Chrome. Some links work fine, some fail without any obvious error. Open your browser's Developer Tools and look at the Console. Mine showed an error about mixed content and serving over an insecure connection. I was able to click the link and download the content I wanted.