https://admin.microsoft.com/Adminportal 400 - Bad Request - Request Too Long

Question

https://admin.microsoft.com/Adminportal 400 - Bad Request - Request Too Long

Martin 5

Bad Request - Request Too Long

HTTP Error 400. The size of the request headers is too long.

Fresh Firefox install:
User's image

I tried chrome and safari as well User's image

I cleaned up cookies, wiped browser history

What is left?, even tried https://login.microsoftonline.com/common/oauth2/logout to logout from everything
I rebooted my PC

What the heck is going on

And all of this started because Microsoft stopped attaching Invoices to their invoice mail.. which is bonkers btw so thanks for that now i monthly has to login to my account to manually download the invoice instead of the old method where you just sent it to me and my invoicing happened automatically...

Chris 0 Reputation points

2026-07-30T21:02:02.56+00:00

I have been having this issue as well for 2 days.

I am only able to connect when using a hotspot while using Edge in InPrivate.I can't connect when on our work network

I have reset all accounts and still nothing.

Chrome - no in both regular and incognito.

Thank you.
Vergil-V 16,990 Reputation points Microsoft External Staff Moderator

2026-07-31T13:57:33.9533333+00:00

Hi @Chris
Thank you for sharing.

From the information you've shared, this behavior appears to be related to your work network.

With that in mind, could you please confirm whether other devices connected to the same work network are able to access the admin portal successfully?

If possible, could you also reach out to your network administrator and ask them to investigate this further?
Lazenby, Jason 0 Reputation points

2026-07-31T15:31:34.8733333+00:00

Started seeing the same issue over the weekend (7/26) when I was attempting to log into Admin center from a remote workstation. Tested on/off the VPN, Inprivate & Incognito, and still Error 400. Desktop in house was working fine until my workstation rebooted for updates, and now I'm seeing the same thing on there. Suggestion was to remove any unnecessary groups (hybrid setup), so I cleaned out what I could from local AD and ran a delta sync, revoked my sessions and still am unable to get into MS admin center. Seems to just be an issue with MS admin center as I'm able to get into Azure, Exchange Admin, Sharepoint Admin, Teams admin, and Intune without issue.
Chris 0 Reputation points

2026-07-31T16:50:56.6866667+00:00

@Lazenby, Jason

Same.

I can access all other admin centers.

Yes, for now, other users on their computers on our work network are able to access MS Admin Center.

I have had the admin log me out of all sessions and that didn't so anything.

Work desktop I can only access Microsoft Admin Center - Active users when using Edge in InPrivate browsing.

When I try to view Licenses and app for a user, I get this.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN""http://www.w3.org/TR/html4/strict.dtd"> <HTML><HEAD><TITLE>Bad Request</TITLE> <META HTTP-EQUIV="Content-Type" Content="text/html; charset=us-ascii"></HEAD> <BODY><h2>Bad Request - Request Too Long</h2> <hr><p>HTTP Error 400. The size of the request headers is too long.</p> </BODY></HTML>

So, I can get further on one computer then another.

I tired logging into Microsoft 365 Admin Center on another users computer in Edge and immediately got Bad Request error.

I tried InPrivate and I was able to view all Active users and no error when viewing Licenses and apps.
Zoë Walker 0 Reputation points

2026-08-03T22:43:13.5266667+00:00

I had this issue for days and tried everything I could think of to fix it. It worked after clearing cache at my house but never in the office at work.

I went into my admin account in Entra ID (since I could still access this site) and checked my administrative roles. I had Global Administrator and then heaps of other extraneous roles. I decided to remove all except Global Administrator and tried the M365 admin centre again. It worked immediately!
iLink Solutions 0 Reputation points

2026-08-05T18:13:46.0133333+00:00

I am having the exact same problem. I tried all the suggestions above, and tried logging in from my phone instead of my work computer and still got the same error message. @microsoft why is this happening, and how can it be fixed? There are matters pending to be taken care of because we can't log in to the Global admin site.
Lazenby, Jason 0 Reputation points

2026-08-05T19:02:33.8833333+00:00

I was able to find a resolution. I had another global admin remove several of the roles that my admin account had that I didn't use, or didn't believe my admin account needed access to. Gave it 30 minutes and then was able to log back into admin center on my desktop. MS Admin center > Active Users > [admin account] > Manage Roles. If you don't have another global admin, you may have to generate a temporary one to login and remove those roles.

1 answer

Your answer

Chris 0 Reputation points

2026-07-30T21:02:02.56+00:00

I have been having this issue as well for 2 days.

I am only able to connect when using a hotspot while using Edge in InPrivate.I can't connect when on our work network

I have reset all accounts and still nothing.

Chrome - no in both regular and incognito.

Thank you.
Vergil-V 16,990 Reputation points Microsoft External Staff Moderator

2026-07-31T13:57:33.9533333+00:00

Hi @Chris
Thank you for sharing.

From the information you've shared, this behavior appears to be related to your work network.

With that in mind, could you please confirm whether other devices connected to the same work network are able to access the admin portal successfully?

If possible, could you also reach out to your network administrator and ask them to investigate this further?
Lazenby, Jason 0 Reputation points

2026-07-31T15:31:34.8733333+00:00

Started seeing the same issue over the weekend (7/26) when I was attempting to log into Admin center from a remote workstation. Tested on/off the VPN, Inprivate & Incognito, and still Error 400. Desktop in house was working fine until my workstation rebooted for updates, and now I'm seeing the same thing on there. Suggestion was to remove any unnecessary groups (hybrid setup), so I cleaned out what I could from local AD and ran a delta sync, revoked my sessions and still am unable to get into MS admin center. Seems to just be an issue with MS admin center as I'm able to get into Azure, Exchange Admin, Sharepoint Admin, Teams admin, and Intune without issue.
Chris 0 Reputation points

2026-07-31T16:50:56.6866667+00:00

@Lazenby, Jason

Same.

I can access all other admin centers.

Yes, for now, other users on their computers on our work network are able to access MS Admin Center.

I have had the admin log me out of all sessions and that didn't so anything.

Work desktop I can only access Microsoft Admin Center - Active users when using Edge in InPrivate browsing.

When I try to view Licenses and app for a user, I get this.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN""http://www.w3.org/TR/html4/strict.dtd"> <HTML><HEAD><TITLE>Bad Request</TITLE> <META HTTP-EQUIV="Content-Type" Content="text/html; charset=us-ascii"></HEAD> <BODY><h2>Bad Request - Request Too Long</h2> <hr><p>HTTP Error 400. The size of the request headers is too long.</p> </BODY></HTML>

So, I can get further on one computer then another.

I tired logging into Microsoft 365 Admin Center on another users computer in Edge and immediately got Bad Request error.

I tried InPrivate and I was able to view all Active users and no error when viewing Licenses and apps.
Zoë Walker 0 Reputation points

2026-08-03T22:43:13.5266667+00:00

I had this issue for days and tried everything I could think of to fix it. It worked after clearing cache at my house but never in the office at work.

I went into my admin account in Entra ID (since I could still access this site) and checked my administrative roles. I had Global Administrator and then heaps of other extraneous roles. I decided to remove all except Global Administrator and tried the M365 admin centre again. It worked immediately!
iLink Solutions 0 Reputation points

2026-08-05T18:13:46.0133333+00:00

I am having the exact same problem. I tried all the suggestions above, and tried logging in from my phone instead of my work computer and still got the same error message. @microsoft why is this happening, and how can it be fixed? There are matters pending to be taken care of because we can't log in to the Global admin site.
Lazenby, Jason 0 Reputation points

2026-08-05T19:02:33.8833333+00:00

I was able to find a resolution. I had another global admin remove several of the roles that my admin account had that I didn't use, or didn't believe my admin account needed access to. Gave it 30 minutes and then was able to log back into admin center on my desktop. MS Admin center > Active Users > [admin account] > Manage Roles. If you don't have another global admin, you may have to generate a temporary one to login and remove those roles.

Answer 1

Hi @Martin

At my end, I am still able to access the admin portal.

With that in mind, could you please check whether you have access to another device, such as a mobile phone or tablet, and try signing in to the admin portal from there?

In addition, could you try using your mobile device as a hotspot and then access the admin portal from your Mac?

Could you also let us know if the same behavior occurs when using a newly created Mac user profile?

If you have any updates, please feel free to share them with us.

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