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

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Posted on by 3BHServices

Hi All,

Just recently having some difficulty connecting power automate desktop to browser flows. I am getting the following error only in the last few days: HTTP Error 400. The size of the request headers is too long.

Any ideas on what i can try to sort this out?

Much appreciated,

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Building flows

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stampcoin 5,146 Super User 2026 Season 1 on at

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@3BHServices Hi,

Please Clear the site’s cookies or Clear the browser cookies, and try it again.

If the works, consider doing so regularly .

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3BHServices 2 on at

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@stampcoin Hi thanks for your reply,

Tried refreshing the cookies, for both chrome and edge, and tried again with no luck. The image below is what I am getting: Failed to create OAuth connection: SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

Let me know if i should try something else. thanks for your help.

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stampcoin 5,146 Super User 2026 Season 1 on at

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@3BHServices Hi,

If you tried clear the cache or used private mode of the browser,

another try is use your domain account to logon the flow.

if you can, your connection (defined) may have problem.

Try with your domain account to see if that works or not.

edit as below:

Check your Powe automate machine runtime on the PC, if it connects to your environment. and use Troubleshoot tool if necessary.

And Check the Machines on https://make.powerautomate.com , you should see it one the left menu list. There are quite much info you can check as well.

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