Works for new and prior accounts, but the account cannot be in a current free trial - it needs to be either finished with one trial or you need to create a different account to use the code.
This works for both on the Essential and the Premium plans.
Thru 1/3/22 (Monday), use code TEENWOLF for Two months
-or-
Thru 1/31/22, use code AFTERSHOW or MAYOR for One month
https://www.paramountplus.com/account/signup/pickplan/
Don’t forget to cancel before the free trial is over or you’ll be billed. You can cancel right away, and you’ll still have access for the full 1 or 2 months (gotta believe they’ll stop allowing that at some point!)