Red Giant subscription licenses have been merged into my.maxon.net accounts as of mid-2021, and are managed via the Maxon App.
When you launch the Maxon App for the first time, you’ll need to sign in with your MyMaxon account using whatever email you'd used to purchase through redgiant.com. Use the Forgot Password option if you don't recall what password you'd used to setup your my.maxon.net account.
For serial licenses, you'll need to head into the top right menu of the Maxon App to import your serial numbers.
Serials purchased from redgiant.com can be found under the Manage section of your my.maxon.net account under the Legacy section.