No PS Plus subscription available on PS3 and PS Vita from June
From June onwards, it will not be possible to purchase a PS Plus subscription on PlayStation 3 or PlayStation Vita.

With the emergence of new subscription forms for PlayStation Plus, the online service will change quite a bit. According to Sony, it’s also time to permanently close a number of doors. The Japanese company has confirmed that from June it will no longer be possible to purchase a PS Plus subscription on PlayStation 3 or PlayStation Vita.
It will still be possible to subscribe via your desktop, mobile device, PlayStation 4 and PlayStation 5, and this will continue to download and play previous benefits such as PlayStation 3 and PlayStation Vita games. With this decision, Sony takes the next step in deprecating old consoles and handhelds.
At the beginning of October last year, a number of payment methods such as PayPal and credit card payment were disabled in both the PlayStation 3 and Vita Stores. While PlayStation Vita games are an obvious shortcoming, it will soon be possible to stream older games via PlayStation Plus Premium.