MacBook Pro (mid 2014) won't upgrade macOS past Yosemite, App Store shows 429 error

Re: macbook pro (mid 2014) wont install past Yosemite 10.10.5.

Seems upgrading MacOS needs to be done in small increments, for each upgrade is a major one. ie: OS X Yosemite 10.10.5 to OS X El Capitan 10.11.6 to macOS Sierra 10.12.6 to MacOS High Sierra 10.13.6 to macOS Mojave 10.14.6

These earlier MacOS versions use 32 bit apps

For tips: Apple Support's article may assist with earlier versions on upwards

How to download and install macOS

Eg: says:

"Download via web browser

1. Make sure that the Mac you’re using to download macOS is compatible with that macOS. If it isn't compatible, you won't be able to complete these steps. 
2. Use these links to download a macOS disk image (.dmg) file. If these links don't work as expected, try again using Safari, which is in the Applications folder.

• • Sierra 10.12
  • El Capitan 10.11
  • Yosemite 10.10
  • Mountain Lion 10.8
  • Lion 10.7

3.By default, Safari downloads the disk image to your Downloads folder, which you can open from the Dock or the sidebar of a Finder window. Learn more about downloading with Safari.

4.Double-click the .dmg file to open it and see the package (.pkg) file within. 

5.Double-click the .pkg file, then follow the onscreen instructions to install the macOS installer into the Applications folder.

6.Open the Applications folder and double-click the macOS installer, named Install [Version Name]. Follow the onscreen installation instructions.

If needed: User Tip: from Community member: Upgrading or updating your Mac

Eg: says:

Troubleshooting macOS updates/upgrades

Although it is rare, it can occur that running a software update or upgrade is not going as expected. The first step you can try is to boot your Mac in to the safe mode, and try to run the update from the safe mode. Starting up your Mac in safe mode can help you identify whether issues you’re experiencing are caused by software that loads as your Mac starts up.

Startup Intel Mac in safe mode

1. Turn on or restart your Mac, then immediately press and hold the Shift key until you see the login window.
2. Log in to your Mac.
3. You might be asked to log in again.
4. On either the first or second login window, you should see “Safe Boot” in the menu bar.

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If you plan on upgrading further than macOS Sierra:

About 32-bit app compatibility with macOS High Sierra 10.13.4 and later:

"Apple worked with developers to transition their apps, and in 2018 Apple informed them that macOS Mojave 10.14 would be the last version of macOS to run 32-bit apps. Starting with macOS Catalina, 32-bit apps are no longer compatible with macOS”. 32-bit app compatibility with macOS

There's a free (non-Apple) app to help transition from 32 bit to 64 bit apps

https://www.stclairsoft.com/Go64/

Apple support's online article: Identify your MacBook Pro model

Eg: says: For MacBook Pro (mid 2014) for 13-inch and 15-inch models

"Newest compatible operating system: macOS Big Sur"

So macOS Mojave 10.14.6 to macOS Catalina 10.15.7 to macOS Big Sur 11.7 is a possibility, if you don't need access to any 32 bit apps.

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Re: "App Store shows 429 error"

Seems the "429 client error" just means the server needs to receive only as many requests as it can handle, not an excessive amount.

You may want to try using the download links for earlier MacOS versions as listed in the above linked Apple Support article : "How to download and install macOS"

This is probably a certificate failure. Older certificates won't work anymore. You'll have to download an installer separately and create a bootable installer following instructions here: https://support.apple.com/101578

Don't spend any time on MacOS older than 10.10 El Capitan, because older versions have encryption that is just too old to be helpful.

If you have Yosemite installed and working use the links in this article to download using Safari browser.

https://support.apple.com/en-us/102662

Follow the directions faithfully, because the process of download and opening succeeds only in PLACING the "Install MacOS...App" in the /Applications folder, so that it can THEN be installed.

SSL to TLS:

In June 2015, Researchers at standards organizations formally declared that Secure Socket Layer (then SSL 3) Internet Encryption was not nearly as secure as was thought, and needed to be replaced. SSL Versions 1 and 2 had already been deprecated by that time,

Early versions of Transport Layer Security (TLS) were already available in many Browsers. Over a remarkably brief period of time, sites tightened requirements for what was acceptable for encryption, and refused connections from browsers that could only offer SSL 3.

Apple issued Safari version 9 in 10.11 El Capitan version of MacOS, which included an early version of TLS encryption. Safari 9 was later provided by Security Update into the two previous versions of MacOS. 10.10 Yosemite and 10.9 Mavericks, PROVIDED you applied all available software updates.

MacOS versions older than those can not make secure [httpS:] connections on the Internet, because by 2016 standards, your proffered encryption (SSL) is considered inadequate.