To link your CD Project Red account with mod.io, follow these steps:
First, ensure that you are logged in to the correct mod.io account on the mod.io website. You can confirm the currently logged in account by visiting this page:
https://mod.io/me/account#basics
Once you have confirmed you are logged in, you can link your CDPR account by visiting the following link and following the prompts to connect your CDPR account.
https://mod.io/g/the-witcher-3?portal=studio
Once completed, your CDPR account will be listed with your linked accounts on the linked accounts page:
https://mod.io/me/account#linked