Error with teams log in on mobile app

Question

Error with teams log in on mobile app

Shania A 25

Repeated error logging into Teams on mobile app using work email. When signing in with my work email, it takes me to my organisations log in portal, however, after logging into that it automatically produces an error saying "header field request too long". I have attached screenshot of the error I receive.

I have cleared cache and data from the app as well as the cookies from the default browser that it may be trying to open my company's login portal. The error remains.

Desktop Teams works fine, it's just when using the app on my phone.

Any assistance would be appreciated 1000052630

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Answer 1

Jade Ng 15,665 Microsoft External Staff Moderator

Dear @Shania A

Good day. Thank you for reaching out to Microsoft Q&A Forum. We are happy to help you!

I'm sorry to hear that you're experiencing issues logging in to the Teams mobile app. The error message you're receiving indicates that the request header field is too long.

For better assist, please kindly let me know:

Are they impacted users, internal contacts or external (guests, federated users, etc.)?
Could you please let me know if you are an admin or end user? If you are the only Teams admin experiencing this issue, or if other Teams admins are encountering it as well?

First, I recommend checking this article to see if it helps: HTTP 400 Bad Request (Request Header too long) responses to HTTP requests

If the above steps don't work, I suggest removing the Teams Administrator for the associated account and adding the permission again. You can also try creating a new Team administrator and checking on your device. (If you are the user, please contact your IT admin to do this).

Looking forward to your response.

Your understanding and co-operation are highly appreciated. Thanks for your precious time. Have a nice day!

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Jade Ng 15,665 Reputation points Microsoft External Staff Moderator

2025-07-22T23:48:18.75+00:00

Dear @Shania A,

Good day. It has been a while, and I am writing to see how things are going with this issue. Just checking in to see if the above information was helpful. If you have any further updates on this issue, please feel free to post back.

Your understanding and co-operation are highly appreciated. Thank you very much for your valuable time and your cooperation

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Jade Ng 15,665 Reputation points Microsoft External Staff Moderator

2025-07-25T03:46:18.47+00:00

Dear @Shania A,

I hope this message reached you.

This is my second time reaching out to check if your issue has been resolved. I really want to make sure your experience is as smooth as possible. If your issue persists or if you encounter any new difficulties, please share more details about the current steps you are taking. I am always happy to assist you whenever you need.

While waiting for your response, I will also be monitoring other customer questions on the forum to assist them. If you have any further questions or updates, please tag (@JadeNg) in the reply so I can assist you more promptly and thoroughly.

I look forward to hearing from you soon.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Shania A 25 Reputation points

2025-07-27T23:20:08.94+00:00

Hi @Jade Ng thank you for suggestions and apologies for the delay in response. To answer your questions, I am unaware if others are affected, I am an internal end user not a Teams admin. I did have a read of the article that was linked, however, unfortunately this is beyond my scope and permissions. It sounds like I may need to contact my IT team to resolve this. Thank you for your assistance with this.
Jade Ng 15,665 Reputation points Microsoft External Staff Moderator

2025-07-28T01:47:34.8866667+00:00

Dear @Shania A,

Thank you for getting back to me!!

You're welcome and no worries at all. I'm happy to hear that your issue was resolved smoothly.

For other questions, feel free to add your post to the Microsoft Q&A forum.

Greatly appreciate again for your patience and understanding.
MODICA Fabrice 0 Reputation points

2026-07-15T20:05:34.29+00:00

Hello, I'm experiencing the exact same issue as described above by OP (Unable to access ms teams on work account on my mobile, being an end user and not an admin, + my IT department won't help me fix it since I'm using my personal phone to log into teams and not work phone). I have uninstalled the app, many times, cleared cache, data, restarted my phone. Computer version works just fine.

I feel like the issue started 4 days ago when I was added to a MS group by a supplier. I could change account back and forth on my computer but it seems my mobile authentication app doesn't like that. I tried deleting the other account the supplier adding me into but nothing has changed.

Anybody would be able to help?

Thanks a lot.
Jade Ng 15,665 Reputation points Microsoft External Staff Moderator

2026-07-17T04:52:27.72+00:00

Dear @MODICA Fabrice,

As I mentioned above, this issue requires assistance from your organization's IT administrator. I recommend contacting them again and asking them to perform the troubleshooting steps on your behalf.

First, I recommend checking this article to see if it helps: HTTP 400 Bad Request (Request Header too long) responses to HTTP requests If the above steps don't work, I suggest removing the Teams Administrator for the associated account and adding the permission again. You can also try creating a new Team administrator and checking on your device. (If you are the user, please contact your IT admin to do this).

Thank you for your cooperation and understanding.