Just to help anyone avoid this pain of changing passwords and infuriation trying to install OSX (in this case Yosemite on an old Mac) you need to enter the correct credentials the first time and when you get your message that it is incorrect and your other device gives you your six figure code, you must append the code on the end of your password and then it will be accepted.

I had tried typing in jus the code and changing AppleID passwords and all sorts!!!

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Oh No!

Now it is saying 'the item is temporarily unavailable' please try again later.

I had to:

Quit installer and then either:

1. Restart and hold down option and command and R and reinstall from the internet

or 

2: Click 'get more help online' and log into safari and into iCloud as my appleid in apple.com and then go back to the install and it let me continue...

This only works if your OSX version and Mac are reasonably new./ It won't open iCloud if it is an old OSX

I think the error is because I didn't buy OSX separately - I just bought my Mac.

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Oh dear - neither of these worked in the end. I tried:

Command + Option + R which is supposed top load the latest compatible OSX but doesn't

Shift + Option + R which is supposed to load the originally shipped version of OSX that came with the Mac but doesn't

Now it just boots into the install screen and can't download OSX or login to iCloud as Safari it too old.

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OK so having downloaded El Capitan  onto another Mac (running Monterey) I then double clicked the Install (InstallMacOSX.dmg) file and then double clicked the PKG file within it and installed the El Capitan installer onto my Macbook (which does not install the OS, just the installer)

I then checked that the El Capitan Installer app was in the \Applications folder on the Macbook and it was.

I then changed the name of my 8GB USB stick (plugged into the Macbook) to 'MyVolume' and ran the following command from the Apple site  instructing how to make a bootable USB:

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

Which then wrote the USB stick successfully although it did take quite a long time. I safely ejected the USB from OSX first, and then removed it physically. Then I plugged it into the old iMac.

I then restarted my iMac with the option key held as soon as the chime sounded. I was given the choice between the Mac disk and the El Capitan installer, I chose the latter.

The USB disk was signalling activity and the progress bar with the Apple sign was displayed. This again took a long time. The progress bar the restarted and I was presented with the dreaded Mac Utilities screen again, but this time the Install OSX option had a slightly different icon.

I chose this option and was presented with the OS X El Capitan Installer.

I proceeded to install OSX El Capitan to the Mac Disk which appeared to work as hoped. I could now see the full graphical OS X El Capitan installer screen with a progress bar at the bottom. 

I will post back what happens.


 

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The screen has reverted back to the dreaded Apple sign with a bite out of it with the progress bar below.

It started off saying 12 minutes but now says that it will be 25 minutes.

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OK so it has finally installed El Capitan and I am at the choose language screen.

It was just about worth it..!

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