PlayStation Ps plus promo code?

I have a question. I bought a ps plus promo code for 14 days because I don't want it any longer and when I redeem it an error occurs and the code is inactive. Why is that and can I do it remedy

Either the code has already been used or you have taken a trial subscription.

As far as I know, there hasn't been a free month or something like that for a long time, but I don't know what it looks like with such codes.

The promo code for the 14 days is actually free with the console. The code can only be used by people who have never used a code before.