Paste them directly into the ux0:data/retroarch/system/ folder. Do not put them into subfolders unless specifically required by a specialized core.
Every core in RetroArch requires specific system files with strict naming conventions and exact MD5 checksum hashes. If a file is named incorrectly or capitalized wrong (e.g., .BIN vs .bin ), RetroArch will fail to detect it. bios files for retroarch ps vita link