If you’re seeing the dreaded “Error 400: invalid_request” when trying to access Gmail through Apple Mail on your Mac, you’re not alone. This frustrating issue has become increasingly common — especially for users running older Intel-based Macs or outdated versions of macOS.
But here’s the truth: this isn’t just a glitch. It’s a sign that your Mac may no longer meet modern security standards — and it is time to move forward by investing in a new Apple Mac Computer.
Why This Error Happens
Google has tightened its security protocols with what is called OAUTH Version 2.0, requiring apps like Apple Mail to use OAuth 2.0 authentication. Unfortunately, many older Macs — particularly those running macOS High Sierra, Mojave, or Catalina — don’t support the latest version of this protocol hence the error message.
As a result, when you try to sign in to Gmail through Apple Mail, or you have changed your Gmail password then you will be promoted to open either Google Chrome or Apple Safari and with an unsupported macOS version or will not work.
Error 400: invalid_request
This app doesn’t comply with Google’s secure authentication requirements.
Any Workaround (If You Must)
While I no longer support Intel-based Macs, here’s what some users try:
- Enable 2-Step Verification in your Google account
- Generate an App Password for Apple Mail this may no longer work and is unstable and is a very high security vulnerability to use.
- Use Gmail via a web browser or on a iPhone or iPad that has a newer iOS version instead of the Mail Application.
These are short-term fixes — and they’re becoming less reliable by the day.
The Long-Term Solution: Upgrade to Apple Mac Technology Silicon
If you’re still using an Intel Mac, this is your moment to consider upgrading. Apple’s new generation of Macs — powered by Apple Silicon (M1, M2, M3, and M4) — are faster, more secure, and fully compatible with modern services like Gmail, iCloud, and Apple Mail, and you can use a Passkey to sign into your Google Account, a Passkey has no password and is the best way to protect and to sign into a Google account.
On-Site Google and Apple Mac Help — Across London and Central London.
Keith Thomas is based in London and provide on-site Apple and Google Mac support for discerning clients who want things done properly — no call centres, no hardware repairs, no fuss.
I regularly visit clients in:
- Central London (Chelsea, Camden, Islington, Notting Hill, Fulham, and more to Surrey)
- Surrey & Berkshire (Woking, Guildford, Esher, Ascot)
- Buckinghamshire & Wiltshire (Gerrards Cross, Beaconsfield, Salisbury)
Whether you’re in a townhouse in Kensington or a country home in Ascot, I’ll come to you.
What I Offer
- Seamless migration from Intel to Apple Silicon Macs
- Setup of Gmail email accounts, Mail, iCloud, and other essential Applications even Microsoft 365 for Mac and Outlook for Mac use with Gmail
- Personalised, jargon-free training and optimisation
I work exclusively with Apple Silicon Macs — no Intel, no hardware repairs, just premium support for modern Apple users.
Ready to Move Forward?
If you’re tired of patchy workarounds and want a Mac that just works — with Gmail, Mail, and everything else — I’m here to help.
Call Keith on 07800 940756
keiththomas.co.uk/contact-us
Let’s get your digital life back on track — the Apple way.