OS X Could Not Be Installed On Your Computer
The operation couldn’t be completed. Undefined error: 0
It doesn’t even explain why.
MacBook Pro 13″, macOS 13.6
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To downgrade from say macOS 10.13 High Sierra to a version of OSX ?
The last version of OSX was Sierra version 10.12 and older
To achieve this would require making a Bootable Installer of OSX that this computer would Qualify to Run
This method will WIPE ALL Data and there is No DATA Recovery - Period.
To perform this action will require booting from a Bootable Installer.
The Bootable Installer can Only be performed on an Apple Computer
This will have to be performed from a Qualifying Computer to run the version of macOS to be made on the Bootable Installer.
Example : Bootable Installer of Sierra would have to be done on a computer that Qualifies to run Sierra.
Notation: If the computer being used to perform this action is Too New or Too Old to qualify to run the version of macOS - this computer can’t be used.
Alternative is, to gain access to a Qualifying Apple Computer from a family member, friend or associate.
Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.
Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive.
It will present options >> Disk Utilities >> View >> View ALL attached Drives.
Choose the Upper Most Drive ( not the volumes indented and list below ).
The drive normally is called Apple Media or Apple SSD - that is the drive to Erase and format as HFS ( Journaled )
Once that is done >> backup out of Disk Utilities and choose install macOS.
Follow the prompts and it may automatically reboot several time.