PlayStation Vita content from the PlayStation Network (PSN) is heavily encrypted. When you use a .pkg file to install a game on Vita3K, the emulator cannot read the data without its matching license. A zRIF string serves as a text-based version of a .rif or work.bin license file, allowing the emulator to "unlock" the game. How to Get zRIF Keys
Are you trying to install a or DLC , and are you getting a specific error message (like "Missing License")? Vita3K - General Guide - RetroDECK Wiki zrif key vita3k exclusive