First, If you go to your My.Presonus account and look at the "My Orders" tab, there is a "Settings button" on the top right, click that and it will give you the option to remove stored card info. Remove the stored card and re-try. Please let us know if this works for you.
Then,
Please use this link: https://shop.presonus.com/products/software/Fat-Channel-Plug-ins/Fat-Channel-Collection-Vol-1-category/Bundles/Fat-Channel-Plug-in-Bundles-Vintage-Channel-Strips-Bundle
Please see the following articles that will help you install the plugins.
Link: https://support.presonus.com/hc/en-us/sections/360000942372-StudioLive-Series-III-Fat-Channel-Plugins