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Although YouTube is constantly evolving and improving, sometimes unforeseen errors can occur. Such is the case with error message 400: “Your customer made an incorrect or illegal request, and we’re going to review it today.

Many users have reported error 400 on YouTube, and while it’s an old and well-known problem, its cause remains a mystery to Google. Let’s take a look at how to fix it.

What is the cause of the YouTube 400 error “client issued an improperly formed or illegal request”?

The YouTube 400 error sometimes seems to be caused by selecting the wrong cookies. However, in most cases, the problem occurs in those versions of Chrome that actively use the Great Suspender extension.
The problem is caused by the way the scroll position is stored in cookies. After a while, the size of the cookie exceeds the limit and the user gets a Youtube 400 error message.

How to fix Youtube 400 error “Client made an invalid or illegal request” message?

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Use incognito mode

Launch Google Chrome browser.
Press the key combination Ctrl + Shift + N to open the incognito window.
Now try to go to the site that caused the mistaken request.

Cleaning the DNS cache

Open the Start menu and look for CMD.
Run the command line as an administrator.
Then type ipconfig /flushdns and press Enter.

Clear your browser cache and cookies

Launch your Chrome browser.
In the address bar, type delete cache chrome actions.
From the drop-down menu, click Clear browser data.
Select Cookies and other site data, as well as cached images and files.
Click Clear data and wait for the operation to complete.

Turn off your browser extension

Launch the Google Chrome browser on your computer.
Visit the Chrome extensions pages at chrome://extensions/.
Activate the disable extension button.
Then disable various extensions, one by one, until the error is fixed.

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Frequently Asked Questions

What does "client made an incorrect or illegal request" mean?

It usually happens because you sent the wrong header in a request to the YouTube server when watching YouTube, it can also happen when the browser tries to use something that has already been cached. Solutions include deleting cookies and cache files from the browser and restarting the browser.

What causes Youtube error code 400?

It seems that Youtube error 400 is sometimes caused by selecting the wrong cookies. However, in most cases, the problem occurs in those Chrome versions that actively use the Great Suspender extension.

How do I fix the YouTube 400 error "Client made an invalid or illegal request"?

Use incognito mode.
Clear your DNS cache.
Clear your browser cache and cookies.
Disable browser extension.

Carter Blakefield