It must be exactly scph5501.bin (all lowercase).
Some shady ROM sites offer dummy files of zero bytes or outdated beta BIOS versions. Always verify the file size: a legitimate SCPH5501.BIN is (512 KB). If it’s any smaller, it’s junk. scph5501.bin missing
The error message scph5501.bin missing typically appears when launching a PlayStation 1 (PS1) game in an emulator. This file is one of the required BIOS dumps for emulating the PS1 console. Without it, the emulator cannot properly initialize the console’s hardware, leading to boot failures or crashes. It must be exactly scph5501
You can your own BIOS from a PlayStation 1 console you own. This requires: scph5501.bin missing