The Collective plugins are available in accounts with a discount for Novation hardware registered. To redeem this discount go to your account page customer.novationmusic.com and then go to the My Software page:
Select your personalised link for the payment plan you want to use:
Then click Buy Now:
Click the purchase button for the plan you selected. In this example "Perpetual" was clicked, so "Purchase Now" should be clicked:
Login using your Novation account details:
Note that the account details you used to register your Novation product are the same ones used to sign in to The Collective website.
Once logged in you'll be taken to checkout and your discount will already be applied:
You can then follow along with the instructions in this article: https://collective-support.focusrite.com/hc/en-gb/articles/360017699840-How-to-subscribe-to-and-install-a-FAST-plug-in