In automation, I have an add-on plan A assigned to plan B when plan B is purchased.
I just had a customer try to sign up for plan B but their credit card declined. Even though their credit card was declined the add-on plan A was still added to their account as active.
This will lead to people getting around the system and stealing content.
Also, I have a Payplans app "jusertype" that assigned the user to the groups that gives them access to paid content when their credit card was declined.