Sony has deactivated pre-paid PS Plus cards to prevent subscription stacking

gamesradar.com:

Several PlayStation players have reported that they are unable to redeem their pre-paid PS Plus and PS Now cards due to Sony reportedly blocking them.

As shared by Push Square, it looks like Sony could be blocking the activation of pre-paid PS Plus and PS Now cards ahead of the PS Plus revamp happening this summer. According to several users online, whenever they’ve tried to redeem pre-paid cards the PS Store just shows an error message that reads: "The pre-paid card could not be redeemed. Please try again later."

@AskPlayStation @PlayStation could you please look into it? The Seller is saying the problem is with you guys, that the codes are active and working, but I can't redeem them, what can I do?April 27, 2022

This could be due to Sony cracking down on those who are attempting to stack subscriptions to get the new PS Plus membership for a cheaper cost. The thinking behind this comes from the fact that PlayStation Now/Plus subscribers will be moved over to PlayStation Plus Premium (the top tier of the PlayStation subscription service) for no additional cost for as long as their current subscription is active. Once it runs out though, you will be charged the new amount.

What some people had planned to do is stack up multiple yearly subscriptions in order to get the cheapest price for as long as they could. PlayStation, of course, doesn’t seem to be a fan of this loophole so has apparently temporarily stopped people from redeeming their pre-paid cards with the intention of doing this. 

According to the Push Square story, Sony Support is responding to players who are confused about why their cards don’t work with something along the lines of: "As of now there is a temporarily deactivated function for PS Plus/PS Now