Can't buy 1 month free on PS4

I kept getting an error when trying to get the 1-month free subscription to Realms Plus for PS4. Also, this is not shown in PSN Store on both PS4 and Playstation website, it's only shown through Minecraft game application. I would appreciate it if Minecraft Realms is purchasable through the Playstation Store on PS4. I would appreciate any help, thank you.