Fixing the HTTP error 400

You might be familiar with the error 404 or the 502 bad gateway error that we discussed prior to this, but the HTTP error 400 is a little more complex compared to the other two.

You might have come across this error once in a while and it might have been a nuisance since it doesn’t always go away without the need for an action from you.

The error 400 is associated with a bad request from the user and even though most of the time it is something that needs to be fixed on the user’s end, something can be wrong on the website’s backend as well.

You might have an issue with the theme on your site and you might need to change it too to solve such issues before they start affecting your website’s performance.

We will talk about fixes for those issues as well, but we guess we should begin with the more common causal agents behind the error 400 and solution to such issues.

What is the error 400?

Before we talk about any issues and the possible ways to solve them, we should probably start with the recognition of an error 400 and its back story to be clear about its causes.

These 400 errors appear to you when you send a request to access some content on a website and it does not make sense to the server. These errors usually correlate to an issue on the user’s end.

The request is sent to the server but it cannot be processed because the server cannot really make sense of whatever it is that you have requested. 

To further understand the concept, we will have to dive deep into the possible causes of the error and the way we can solve these issues to access the content we want to.

Causes of the HTTP error 400

In the following section, we are going to discuss a few possible issues that might be causing the HTTP error 400 on the user’s end and we will also discuss how to fix error 400 with each issue.

1. Browser cache and cookies

Remember the cookies that every website offers you and you leave those crumbles behind to let the website trace you back? They can be a probable cause behind an error 400 that you are encountering.

If you think about clearing the cache and the cookies from your browser, it is somewhat similar to turning your machine off and then turning it on to fix an issue.

If you are lucky enough and the issue was with an expired cookie or some faulty cache, the issue will be solved on its own. Otherwise there are other steps that might be needed.

Moreover, if you receive the error 400, try pressing CTRL/CMD along with the SHIFT key and R key to bypass the error while being on the error screen. If this doesn’t work, move to the next possible fix.

2. Faulty URLs

You might be thinking that faulty URLs always cause the 404 error, but that is not the case. That is the case when the page you requested doesn’t exist at all on the server.

When we talk about a faulty URL causing the error 400, we are talking about a URL that has a syntax issue and the syntax format entered qualifies as an illegal character on the server.

A simple example would have to be the ‘%20’ parameter within the UTM fields in a URL. If the same syntax is added anywhere in between the UTM parameters, the URL stays valid.

In case the same syntax is added before the UTM parameters and into the main part of the URL, the server will automatically display an error 400 for such a request.

This issue correlates to links you might be following through clicks or hyperlinks on webpages. Happened to one of our casino clients namely Turbo casino, and they were able to fix it for the users as well. Make sure the syntax in the URL is valid if you get such an error.

You can double-check your URLs to make sure there is no such mistake in the URL or the syntax within the URL that is causing the 400 error.

3. Broken Add-ons and browser extensions

If you didn’t know, your browser add-ons and extensions alter the behavior of your browsing experience a lot. How do they do it? They are allowed to work on every webpage you access and this adds their vulnerability to every page you visit. Sometimes, these broken add-ons can add to your bounce rate too!

If you have an extension that is not compatible with something on a webpage that you are trying to access, or one of your extensions has gone rogue and is sending invalid requests to a server, you will get the error 400.

You can go to your extensions within your browser and disable them all to see if any of them is causing the error. In case you can access the webpage after disabling the extensions, you can investigate further.

You can turn the extensions off one by one and monitor the behavior of the website to know which extension was causing the error. In case disabling the extensions does not help, proceed to the next possible cause and fix.

4. DNS Cache issues

Although clearing the DNS cache has a similar effect as the browser cache deletion, the two things are unique and separate totally. Your DNS cache is stored on your computer every time you visit a website.

You can erase the DNS cache easily. If you are using Windows, go to the command prompt and simply enter the following command to erase all DNS cache: “ipconfig /flushdns”.

In case you are using a Macintosh, you can search for the terminal and enter the command “sudo killall -HUP mDNSResponder”. In case this doesn’t work, you can try “sudo discoveryutil udnsflushcaches”.

In case this does not fix the issue, you can go on to other possible causes and their fixes.


If you have solved the issue with these possible causes, well and good. In case these didn’t help, you should really contact the server provider or the host. They know more about the problem for sure!

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