How To Fix The 400 Bad Request WordPress Error

Running into a WordPress issue like the 400 Bad Request WordPress error on your WordPress site can be a real speed bump. Sometimes it can appear when you’re trying to log in. It can interrupt your attempt to install a new plugin. Even trying to access specific pages and posts could trigger this error. 

As fellow WordPress admins, we understand the fear of downtime and the frustration of troubleshooting. We recognise that time is of the essence. This article provides simple steps to identify and resolve the reasons behind your 400 error as soon as possible. 

TL;DR: You can fix a 400 error by checking the URL, clearing your cache, or troubleshooting conflicts. But, unplanned fixes can cause more issues than you already have. We recommend that you back up your site with BlogVault first.

What is the 400 Bad Request in WordPress?

When you see a 400 error in WordPress, it means there is a client-side error indicating that the server could not understand the request due to invalid syntax.

Let’s break that down. 

• A client-side error happens when an issue is on the user’s side of the connection with the server. 

• A request is a message your browser sends to the server asking for information or action. 
• If the request is malformed or has incorrect syntax, the server cannot process it. That is when the 400 Bad Request error appears.

Think of a 400 error like sending a letter with the wrong address or incomplete information to the post office. The post office (the server) can’t deliver the letter (the request) because the address (the syntax) is unclear. As a result, your letter is returned to you, just like how a 400 error stops your request from reaching the website.

Some common causes are:

• Wrong or badly formatted URLs lead to server confusion.
• Outdated data in the browser can cause loading or display issues.
• Misconfigurations here disrupt URL handling and permissions.
• Bad or incompatible plugins or themes cause site errors.
• Failed updates of a theme or plugin
• Overusing bandwidth, storage, or processing can lead to errors or slowdowns.

This error can prevent users from accessing specific pages on a WordPress site, leading to potential loss of traffic and user engagement. So, let’s jump talk about how to fix the error now. 

How to fix the 400 Bad Request error?

Encountering the 400 Bad Request error on your WordPress site can be frustrating, but thankfully, it’s often a straightforward issue to resolve. Whether it’s a simple URL error or a more complex plugin conflict, following a structured troubleshooting process will help you get your site back to normal.

1. Check the URL

The first step in fixing a 400 Bad Request error is to check the URL you’re trying to access. Incorrect URLs, such as those with typos, missing slashes, or incorrectly formatted query strings, are common triggers for the error. 

When typing or pasting a URL, make sure it is complete and correctly formatted. Also, ensure there are no unnecessary characters or spaces. A small mistake in the URL can lead to the server not understanding your request, which causes the error. Double-check each part of the URL, including the domain name, path, and any query parameters, to ensure accuracy.

By starting with this basic step, you can often quickly resolve the error or at least rule out this common issue.

2. Log out and log in again

The advice to “log out and log in again” may seem like a tale as old as time, but it’s a simple step worth trying. 

Logging out of your WordPress admin panel and then logging back in can refresh your session data. Session data is the temporary information stored during your interaction with a site, like your login status and preferences, to personalize your browsing experience. Refreshing this data can resolve minor issues that might be causing the 400 Bad Request error. 

3. Make sure the file upload isn’t too large

One common cause of the 400 Bad Request error is failing to upload a file that exceeds the allowed size limit. WordPress and server settings have size restrictions to ensure performance isn’t slowed down by large uploads. If you encounter a 400 error while uploading, check if the file entity is too large. 

To fix this, you can reduce the file size or adjust your server settings to allow larger uploads with WP maximum upload file size. Ensure that you follow best practices when changing these configurations to avoid other potential issues.

If file size is the problem, troubleshooting in this way can lead to a swift resolution and smooth uploads. For more detailed guidance, refer to our article on fixing errors related to file uploads.

4. Identify conflicting plugins and themes

Conflicting plugins or themes can be a hidden cause of issues like a WordPress site crash or the 400 Bad Request error. These conflicts disrupt your site’s operations, leading to unexpected errors. 

To check for conflicts, deactivate your plugins one by one, on the admin panel. Check if the error gets fixed. If deactivating a plugin does fix the issue, it is incompatible with the rest of your site. Reactivate the other plugins once you’re done. 

If it’s not a plugin, switch to a default theme like Twenty Twenty Four. If this fixes the issue, then the previously active theme was the problem. R

Pro tip: If you’re unable to access your WordPress dashboard to manage plugins and themes, you can use an FTP client to solve the problem. Change the name of every plugin folder to deactivate it. For themes, rename your current theme’s folder (e.g., mytheme_old) to force WordPress to revert to a default theme.

Once you identify the conflicting plugin or theme, consider what changed recently to trigger the error. 

• Is it a new plugin? If so, find an alternative. 
• Are there updates available? Then, it’s time to update the theme or plugin.
• If it was recently updated, rollback the plugin temporarily. Reach out to the developers and let them know that you have identified some conflicts. Wait for them to fix the problem before you safely update the plugin or theme again.

5. Resolve conflicts with WP core

Conflicts with the WordPress core can sometimes trigger the 400 Bad Request error, affecting your site’s overall functionality. These conflicts often arise from outdated files or issues during updates. Here’s how to resolve them effectively:

Expert advice: Before making any major changes, use a backup plugin to securely back up your site. This will ensure you can restore it if anything goes wrong.

Start by checking if there was a recent update that could have triggered the error? If there was an update, rollback your WordPress version. The easiest way to do this is to restore a backup. Otherwise, reinstall the older WordPress core files with the following steps: 

1. Access your site via an FTP client and navigate to the root directory. 
2. Download the previous WordPress version from the official WordPress.org site.
3. Extract the files and upload the wp-admin and wp-includes folders to your server, replacing the existing ones. 
4. After replacing core files, visit your site to see if the problem persists. If it’s resolved, then, you know that it was a buggy update that triggered the conflict. Wait for the developers to fix the bugs before you update the core again. 

If it was not an update, then check to see if your WordPress core is outdated. You will have to safely update the core by testing it on a staging site first. 

6. Clear cache

Caching is a process where temporary data is stored to improve website loading speed and performance. Both your browser and WordPress can store copies of web pages or other resources, allowing them to load faster when you revisit a site. By clearing caches and cookies, you ensure that your browser and WordPress fetch the most current data from the server. This way, any troubleshooting you’ve already done will reflect in the cache. 

• Clear browser cache and cookies: Sometimes, your browser holds outdated data that can interfere with site requests. By clearing the cache, you remove these old files, ensuring your browser accesses the latest site data. Deleting cookies can also help, as they can contain corrupted or conflicting information related to your WordPress site.
• Clear DNS cache: The DNS cache stores information about previous web visits. If there’s outdated or incorrect data cached, it can prevent you from connecting properly. Clearing the DNS cache ensures that your computer fetches fresh data directly from the server, aligning with current DNS records.
• Clear WordPress cache: If you use a caching plugin in WordPress, it might be holding onto old data that causes the error. Go to your caching plugin settings and clear the cached WordPress files. This ensures that the latest content and site configurations are delivered to users, resolving potential conflicts causing the error.

How to prevent the 400 Bad Request error?

Dealing with 400 errors on your WordPress site can be time-consuming and frustrating. These errors disrupt your website’s functionality, impacting user experience and productivity. By taking proactive steps to prevent them, you can save yourself the hassle of lengthy troubleshooting 

• Regular updates: Keeping the WordPress core, themes, and plugins up-to-date is crucial for several reasons. Updates often include patches for security vulnerabilities, helping to protect your site from attacks that can cause errors. They also fix bugs and improve compatibility, ensuring that all components work seamlessly together. Regular updates help you avoid conflicts that could otherwise lead to 400 errors or other issues.
• Backup regularly: A reliable backup system acts as an insurance policy for your website. Mistakes, errors, and attacks can happen, and having a recent backup allows you to restore your site quickly without losing valuable data. Regular backups ensure that even if a 400 error disrupts your site, you can revert to a prior state and continue functioning with minimal downtime.
• Optimize database: Over time, your WordPress database can accumulate unnecessary data like post revisions, trashed items, and spam comments. This clutter can slow down your site and contribute to errors. Regular cleaning and optimization of your database keeps it  lean, enhancing overall site performance and reducing the likelihood of syntax issues that lead to 400 errors.
• Use reliable themes and plugins: Not all themes and plugins are created equal. Choosing those that are well-reviewed and consistently updated minimizes the risk of conflicts and compatibility issues. Reliable options are designed to integrate smoothly with WordPress, reducing the potential for errors as components evolve.
• Limit plugin use: While plugins add important functionality, each one increases the complexity of your site. Too many plugins can slow down your site and increase the risk of conflicts. By using only necessary plugins, you reduce the chance of running into errors caused by overlapping or incompatible functionalities.
• Configure .htaccess carefully: The .htaccess file is powerful, controlling how URLs are managed and who can access your site. Misconfigurations in this file can lead to errors that disrupt site access and functionality. Careful editing and proactive backup of the file help prevent problems, ensuring smooth server operations.
• Monitor server resources: Regularly checking your server’s bandwidth, storage, and processing power usage ensures your site operates within its capacity. When your site exceeds resource limits, you may encounter performance issues and errors. Monitoring these resources helps you anticipate needs and facilitate timely upgrades to prevent traffic overloads from causing problems.
• Enable debugging: Enabling WordPress debugging provides valuable insights by generating error logs. This feature helps you identify and address issues early, before they affect users. Debugging is like having a toolbox handy when problems arise, enabling quicker problem-solving.
• Implement security measures: Security is crucial in maintaining a stable site. Hacking attempts and malware can compromise your site’s integrity, leading to errors. Strong security practices and plugins help protect your site, ensuring it remains error-free and reliable.
• Test changes: Before implementing changes on your live site, use a staging environment to test them first. This controlled setting allows you to identify any potential errors or issues without affecting your users. By catching problems early, you keep your live site running smoothly and maintain a great user experience.

Final thoughts

The 400 error in WordPress can disrupt your site’s functionality and impact the user experience. Visitors may find pages inaccessible or information missing, which can affect your site’s credibility and their trust. 

However, if you tackle this error without a plan, things can get worse. Troubleshooting mistakes might lead to further errors or even data loss. That’s why taking a comprehensive backup of your site is crucial before you begin. It gives you a safety net to fall back on if anything goes wrong.

FAQs

How do I fix 400 error in WordPress?

To fix a 400 error in WordPress, start by checking for incorrect URLs or malformed query strings. Clear your browser cache and cookies. Deactivate plugins one by one to check for conflicts, or switch to a default theme to rule out theme issues. Review your .htaccess file for misconfigurations. If these steps don’t work, increase your WordPress memory limit.

How do I fix a 400 bad request error?

Fix a 400 bad request error by ensuring your URL is correct and well-formed. Clear browser cache and cookies, which can contain outdated information. Check for and resolve any plugin or theme conflicts by deactivating them individually. Also, verify and fix settings in your .htaccess file if necessary.

Why is WordPress unable to connect to backend HTTP Error 400?

WordPress may be unable to connect to the backend with an HTTP Error 400 due to incorrect syntax in your request. This could be from misconfigured URLs, plugin or theme conflicts, or corrupted cache and cookies. Checking these elements and following troubleshooting steps can resolve connectivity issues.

What is error 400 in WordPress REST API?

Error 400 in the WordPress REST API means a request has invalid syntax. It often happens with malformed requests sent to the server. Solutions include checking for correct API endpoints and parameters, clearing browser cache, and ensuring any software making the API requests is functioning correctly.

How to fix server error 400 in Elementor?

To fix a server error 400 in Elementor, first clear your browser cache and cookies to remove any outdated data. Check your URL for any mistakes. Deactivate potential conflicting plugins. Make sure Elementor and WordPress are both up-to-date, and review your .htaccess file for any misconfigurations.