Auth 2.0 Error 400 on Mail account

Thank You Animaster. Your solution to get gmail back on Mac Mail worked GREAT! I'm not what I call a computer wizard, but I followed your instructions and it worked. Was ready to buy a new computer as mine is late 2011 but gmail is so painful to use and I have multiple account. But my main one went out. Don't change your password on gmail. That's what caused my main gmail account to go off. Then when I tried to add in mac mail with google it gave me that bs, need Auth 2.0 Error 400. Did't allow me to sync my calendar but just put in under my other gmail account. THANK AGAIN!

None of the solutions provided have worked for me either, it's clearly an issue with the developers!!! PLEASE HELP and fix this problem, they want us to keep our devices secure by updating our passwords regularly ...... then we can't access our mail! DOH!!! CRAZY!!! B

The Animaster has the solution. Well it's not the easiest thing I've ever done but IT WORKS! I copied it just in case I can't get back to it so here it is. The only down side is your gmail on macmail does't connect to the mac calendar. Here is the Animaster SOLUTION & IT WORKS. Don't let the 2 step verification scare you, it's just what it's called & you only do it once to get it to work. Here it is from the Animaster:

I FOUND THE SOLUTION. 

People have mentioned it here, but with incomplete steps. So here is how to get it done:

1.) KNOW why this is happening in the first place: it's coz Google says your old mac and old mac OS have insufficient security. With that said, you can only update an old mac for about 7-10 years. Then you're SOL. Keep that in mind. Lucky for us old mac users (I'm running a 2011 MBPro with ElCapitan) -- we are still able to add new GMAIL accounts with a workaround. 

2.) As mentioned here, open your GMAIL account preferences by signing into GMAIL by web browser and clicking on your avatar in the upper-right and selecting "Manage your Google Account". Then click on the "Security" tab on the left.

3.) Under "Signing in to Google" ENABLE 2-step verification. This alone will NOT fix it, but it WILL allow you use what Google calls "Less Secure Apps Access". If you notice in your account settings, Google automatically sets this to OFF -- essentially blocking access to any apps that Google dubs 'insufficient security'. Enabling 2-step verification will bring up a third line under "Signing in to Google" that says "App Passwords".

4.) Click on "App Passwords" and this will walk you through generating a password that you can use to manually add a GMAIL account with your old mac. 

5.) Select and copy the generated password, go into Apple Mail preferences and select "other" when adding the new email account. Type in your gmail email address, and use the password you copied earlier, in the password field. 

If this helps, PLEASE hit the kudos button to bring it to the top!

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FYI the Avatar is your picture on gmail. Didn't know that term. Keep going IT WORKS & it's better than dealing with the gmail format to read your emails especially if you have multiple gmail accounts. I changed my password on my main email account and that's what triggered the my gmail not working on my mac mail account. So don't do that unless you absolutely have to. Again, thanks to people like Animaster for figuring this out and sharing.

I fixed this...

I went to google settings > security > 2-step verification > app passwords > type in imail and generate a passcode, copy the passcode. Then I went to iMail > add account > select "other mail account" > type in email address and the passcode that was generated with google. Hit enter and it should work.

Thx! I managed to get access to my G mail on my mail using the the process all OK and good but did hit issues as the g mail on my phone then wouldnt accept the Pwd and had to try and change it via g mail. Did so but kicked me out of Mac Mail. Was like vicious tech circle. Seems cant operate g mail using the 'other e mail acct' both on mac mail and also on my phone.

In the end i went for less pain and updated my Mac to OS to Monterrey. Was able to transfer g mails to may mac no problem. Cheers!

This worked for me so much appreciated. I removed my Google account from 'Internet Accounts' first (as could not sign in) before adding it back under 'Add Other Account' as you say with the newly generated password from'App Passwords'. I am using High Sierra 10.13.6.

Thanks for this workaround.

I spent time with 4 Apple specialists, and they were dumbfounded by the error and unable to shed light.

Thankfully, however, one of them suggested ‘googling’ the error, and I landed on this page, which solved the issue.

After much wailing and gnashing of teeth this finally worked for me.

App Password is no longer under "Sign in to Google". Took some searching to find it. After setting up 2-Step Verification it's at "Security/How you sign in to Google/2-Step Verification"...scroll to bottom. But the idiot programmers may have moved it again by now.

Then I tried to open a new email account in Mail with the same email address and it wouldn't let me. Next I thought I would just delete the account and recreate it. I was informed by Mail that this would delete all the data in the account. So I backed up that account emails and then deleted it. Tried to set up a new Gmail account but got the same error message that started all this. So I set up an "Other" account, as suggested, using the same email address as the one deleted and the App Password. This worked. Then I had to wait for over 3000 emails to download. Now my inbox is full of stuff I had trashed. But at least it seems to be working again.

I will now start weaning myself off of all things "Google".

Followed above instructions and got: "This account already exists." So, deleted old email, repeated and it worked. So, remember to delete your old email account before creating a new one with the same address.

I am having this problem with gmail in (or not in) my Mail. I have a Macbook air with the latest updates of Sonoma. Granted I still have some files that date back many years from antique Macs. When I have more time, Iwill try the steps you outline and see if it helps.

For what it's worth, I was able to get it to work by downloading the Chrome browser and setting it as my default browser. Once done, try to log into your Google account like normal. Once all is up and running, you can change your default browser back to Safari. Much easier than setting 'app passwords' like Google is trying to make us do.

I had some issues with changing my password on a newer macbook pro M2 so I deleted the account and went to re-add. The same 400 error is coming up. It can't be just an old mac issue and OS since what I have is newer Mac and OS is 14.3. Something is going on between apple and google causing this issue. I already have dual authentication so can someone help out here?

This worked for me:

I noticed that the popup to login into google, when trying to add a new account, was opening in Safari Private Browsing mode. I went digging in Safari's settings, and in the "Advanced" tab under privacy I turned off the "Use advanced tracking and fingerprinting protection" AND the "Allow privacy-preserving measurement of ad effectiveness" and BAM... I was finally able to get past the 400 error that Google was sending back and I was able to authenticate and add my Gmail account to my Internet Accounts.

I just want to give KUDOs to Animaster for sharing the solution to setting up gmail on an old MacBook. 2013 for me, currently running Big Sur 11.7.4. THANK YOU so much for sharing. I spent several hours today tearing my hair out and nothing worked until I found your post!!!!! Bless you.