Unable to update my MacBook Pro (13-inch, Early 2015) from Yosemite to Monterey due to iCloud/AppleID glitch

For older systems you need to type the code immediately after the password for it to be accepted.

For example: Your password is "hello", and the code you receive is "123456". You would enter the following for your password:

hello123456

See if you can access the Monterey installer download using the link within this Apple article (not sure if you still need to authenticate with the App Store):

How to download and install macOS - Apple Support

There is also a chance you may need to first upgrade to an intermediate version of macOS such as 10.11 or 10.13 before you may be able to install Monterey. I'm unable to find out the minimum OS requirement the Monterey installer has, but I do know that macOS 10.13 introduced system firmware updates and even a new drive layout to support the new APFS file system. AFAIK, the Monterey installer won't convert the old HFS+ file system used by Yosemite to APFS, so installing 10.13 first may be required. Besides, macOS 10.11 may help you to better access the App Store as well and the 10.11 installer is available outside of the App Store so it may be the easiest first step, but carefully read the instructions in the Apple article I linked since there are multiple required steps.

Before you do anything, make sure to have a good backup of your data just in case something goes wrong....people should always have frequent & regular backups anyway.

Hello BlueMR,

Your MacBook Pro does support Monterey. It sounds like the issue may be with the current system or the actual Apple ID or password. You can test signing in to the Apple ID website here: Manage Your Apple ID

If you can sign in successfully there, the issue isn't with the account or password.

If there is an issue with the Apple ID or password, use the following for a solution:

• If you forgot your Apple ID email address or phone number
• If you forgot your Apple ID password

Make sure the Mac is up to date on Yosemite, if needed: Update macOS on Mac

After updating to the latest Yosemite version, try signing in to the App Store once again.

It's also important to note that you will want to backup any data on the Mac that's important before upgrading macOS to Monterey: Back up your Mac Also, be aware of the transition to 64-bit technology and how that affects 32-bit apps: 32-bit app compatibility with macOS High Sierra 10.13.4 and later

Lastly, consider creating your daughter her own user account on the Mac, to avoid any issues moving forward: Set up users, guests, and groups on Mac - Apple Support (Unless this will solely be her device.)

Should the issue continue, can you test the issue in another user account with the steps provided above? That would tell us if the issue is system wide or user specific.

Hoping to hear how it goes.

Take care.

You're welcome. Glad to have helped.