“Invalid JSON Error” in WordPress: Key Causes & Quick Fixes (Beginners’ Guide)

You’re updating your WordPress site with the Gutenberg Block Editor when suddenly, you see an error called “Invalid JSON Response”. This common yet frustrating issue disrupts functionality, slows workflows, and can even harm UX.

JSON errors often stem from malformed code, plugin conflicts, or incorrect data handling. But resolving them doesn’t have to be complicated.

So this blog will shed light on fixing the invalid JSON error in WordPress, from troubleshooting methods to debugging plugins and more. Then your site will be stable and the content will be accessible and engaging. Let’s begin.

What is the “Invalid JSON Response” Error in WordPress?

The “Invalid JSON Response” is one of the most common WordPress errors. It occurs when the server fails to return properly structured JSON (JavaScript Object Notation) data.

This error can break critical functions like the WordPress REST API, Gutenberg editor, AJAX requests, or plugin operations. It may lead to incomplete page loads, missing content, or admin dashboard issues.

But for that, you first need to understand the common causes behind it.

What Causes the “Invalid JSON Response” Error in WordPress?

As the name suggests, the “Invalid JSON Response” occurs due to corrupted or malformed JSON data. That may be due to some common triggers, like:

Plugin Conflicts

Poorly coded or conflicting plugins can interfere with WordPress’s REST API or AJAX requests. That leads to malformed JSON responses. Deactivating plugins one by one helps identify the culprit.

Theme Issues

A faulty or outdated theme may contain broken scripts or improperly handled REST API calls, causing JSON errors. Switching to a default theme (like Twenty Twenty-Five) can help diagnose the issue.

Database Corruption

Database corruption—often due to failed updates or server crashes—can break JSON-structured data retrieval. Running a database repair via wp-admin/maint/repair.php may resolve this.

Server Configuration Problems

Misconfigured servers (missing mod_security rules, incorrect MIME types, or missing HTTPS headers) can block or alter JSON responses. Checking server error logs or consulting your hosting provider can pinpoint the issue.

Incorrect URL Settings

If WordPress Site Address (URL) or Home URL settings are misconfigured (e.g., mixing HTTP/HTTPS), API requests may fail, returning invalid JSON. Verify these in Settings > General.

REST API Issues

WordPress relies on its REST API for many functions. If blocked by security plugins, .htaccess file rules, or server firewalls, JSON responses may break. Testing the REST API via yoursite.com/wp-json/ helps confirm this.

Syntax Error in JSON Data

Custom code (hooks, API integrations, or theme functions) with incorrect JSON formatting can trigger parsing errors. A debug log (WP_DEBUG) or JSON validator can help detect malformed data.

PHP Version Incompatibility

Older PHP versions (below 7.4) may struggle with modern JSON handling, leading to parsing failures. Upgrading to PHP 8.0+ (recommended for WordPress) often resolves this.

Identifying the exact cause is crucial for applying the right fix. For that, hiring professional WordPress developers will be more suitable.

How to Fix the Invalid JSON Error in WordPress?

As seen above, there are several trigger factors for invalid JSON errors in WordPress. So you have to determine the root cause and troubleshoot error “Updating Failed. The Response is Not a Valid JSON Response.” accordingly. But here are 9 ways to fix the invalid JSON error in WordPress.

Check SSL and Mixed Content Error

Mixed content refers to a situation where your website serves both secure (HTTPS) and non-secure (HTTP) content on the same page. Browsers often block mixed content for security reasons, which can lead to issues with invalid JSON response errors in WordPress.

Here’s how you can identify the mixed content on your website:

Step 1: To pinpoint mixed content issues, open your website in a web browser.

Step 2: Right-click anywhere on the page and select “Inspect Element” or “Inspect”.

Step 3: Go to the “Console” tab, which will display any mixed content errors.

Step 4: You may see messages like the following, indicating the source of the problem.

“Mixed Content: The page at ‘https://example.com’ was loaded over HTTPS, but requested an insecure resource ‘http://example.com/…'”.

After identifying the mixed content error, you can work on fixing it through the following techniques:

• Update Content Links: In your WordPress database, there might be links to HTTP resources (e.g., images, scripts, stylesheets) that need to be updated to use HTTPS.
• Update Theme and Plugin Files: Inspect your theme and plugin files for hardcoded HTTP links and update them to use HTTPS.
• Use Relative Paths: Whenever possible, use relative paths for your resource links, like “/wp-content/uploads/image.jpg” instead of “http://example.com/wp-content/uploads/image.jpg”.
• Use HTTPS URLs: Whenever you add links or resources, ensure you use “https://” instead of “http://.”
• Content Delivery Network (CDN): If you’re using a CDN, make sure it’s configured to serve resources via HTTPS.
• Update Third-Party Scripts: If you’re including third-party scripts on your site (e.g., Google Fonts, Google Analytics), check their integration code and ensure it’s configured for HTTPS.

• WordPress Settings: Go to “Settings” → “General” in your WordPress dashboard and make sure both “WordPress Address (URL)” and “Site Address (URL)” use HTTPS.

After making these changes, clear your browser cache and revisit your website. Open the browser’s developer console (F12 or right-click and “Inspect”) and check for any remaining mixed content errors in the console. Resolve any that still appear.

Once you’ve resolved mixed content errors and no longer see any issues in the console, test the JSON functionality in your WordPress site to ensure the “Invalid JSON Error” is resolved.

Disable the Block Editor and Switch Back to Classic Editor

Since WordPress 5.0, Gutenberg has been the default editor for the CMS. Along with the several benefits, this editor may also result in the JSON response error. So to fix the invalid JSON error in WordPress, you may try using the Classic Editor. 

First, follow the WordPress plugin installation process and activate the Classic Editor. Then, open the WordPress settings and navigate to “Writing”. After that, under “Default editor for all users”, select “Classic Editor” and save the changes.

With the Classic Editor now set as the default editor, go back to the post or page where you were encountering the “Invalid JSON Error.” Edit the post/page as you normally would, but now you’ll be using the Classic Editor instead of Gutenberg.

Save or update the post/page. Check if the “Invalid JSON Error” still occurs while using the Classic Editor. If yes, you can move to other methods I have mentioned in this guide.

Resolve WordPress REST API Conflict

The invalid JSON error in WordPress may be due to the way the editor communicates with the server, i.e. through the REST API. 

To investigate this error, you can utilize the WordPress Site Health tool, which provides insights into the health and performance of your website. To access it, go to “Tools” and select “Site Health”.

In the Site Health tool, you may encounter an issue labeled “The REST API encountered an unexpected result.” Clicking on this issue will provide you with additional information and clues that can help you determine whether a plugin or third-party service is causing the problem. If the problem is due to a plugin installed on the website, you may follow the method for the same, mentioned later.

Change the WordPress Permalink Structure & Regenerate the ‘.htaccess’ File

Modifying your WordPress permalink and then updating the .htaccess file accordingly can be an excellent way to fix the invalid JSON error in WordPress.

First off, you need to take back up of your WordPress website. Here’s the step-by-step guide for the same:

Step 1: Log into your WordPress admin dashboard.

Step 2: Go to the “Settings” section in the left-hand menu and click on “Permalinks”.

Step 3: In the Permalinks settings page, you’ll see several options for configuring your site’s URL structure. Choose a new WordPress URL structure from the available options.

Common choices include “Post name”, “Day and name”, and “Month and name”. Select the one that best suits your website’s SEO and content structure.

Step 4: After selecting a new permalink structure, scroll down the page and click the “Save Changes” button to apply the new settings.

If there’s still an invalid JSON error in WordPress, you may have to generate a new .htaccess file to ensure it reflects the new URL structure.

Step 5: But first, access your website’s file and directory structure through an FTP client or the WordPress hosting provider.  Find the .htaccess file and create a backup.

Step 6: Now, download the .htaccess file and open it with a code editor.

Step 7: Next, replace the old code with the one mentioned below:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

Step 8: Then, save changes and upload it back to the WordPress root directory of your website.

Step 9: After changing the permalink structure and regenerating the .htaccess file, visit your website and perform the actions that previously triggered the invalid JSON error in WordPress.

If it is resolved, it indicates that the error might have been related to the previous permalink structure or issues with the .htaccess file.

But if it still persists, you can either keep the new structure or revert to the old one. If you want to change back to the older structure, visit the Permalink settings and select it. You may even revert back to the older .htaccess file.

The .htaccess file is a part of the core platform. So if you’re not comfortable with this step, look for dedicated WordPress programmers.

Check the Themes and Plugins

Issues related to themes and plugins can often lead to conflicts that trigger this error.

Step 1: Log into the WordPress admin dashboard.

Step 2: Go to the “Plugins” section in the left-hand menu.

Step 3: Select all the plugins by checking the box at the top of the list. From the “Bulk Actions” dropdown menu, choose ‘Deactivate’ and click the ‘Apply’ button.

Step 4: After deactivating all plugins, visit your website and perform the actions that were previously triggering the invalid JSON error in WordPress. Check if the error persists. If it’s resolved, you’ve identified that the error was likely caused by one or more of your plugins.

Step 5: To identify the specific plugin causing the conflict, reactivate your plugins one by one and test your website after each activation.

If the error is due to a plugin conflict, it will recur when you activate the problematic one. Deactivate it again. For the error-causing plugin, check for updates. Outdated or incompatible plugins can lead to errors. So update the problematic plugin to its latest version.

You may also contact the plugin developer or opt for an alternative. If you can’t find a better alternative, I suggest you opt for our WordPress plugin development services. We’ll create an excellent plugin for your website.

Moving on to the theme. Sometimes, themes can also cause conflicts that result in JSON errors.

Step 6: Temporarily switch to a default WordPress theme like Twenty Twenty-One. For that, you will need to follow the WordPress theme installation process.

Step 7: Test your website with the default theme to see if the error persists. If the error disappears with the default theme, it suggests that your previous theme might be the culprit. Then you will need to either contact the theme developer or find an alternative.

But like the plugin, if you are looking for something personalized with the design, our WordPress theme development services are just for you.

However, if the theme isn’t the culprit, you can revert back to the theme you had previously.

Temporarily Disable the Security Firewall

Setting up a WordPress firewall is among the most significant security techniques. But they can sometimes be overzealous and may erroneously block certain actions or API requests. That causes issues like the invalid JSON response.

So to fix the invalid JSON error in WordPress, disable the security firewall temporarily.

Step 1: To start with, identify the security firewall or plugin installed on your website. Some of the best WordPress security plugins are Sucuri Security, Wordfence, ithemes Security, etc.

Step 2: In the dashboard, find and access the settings for your security firewall plugin.

Step 3: Look for an option to temporarily disable the firewall or put it into a maintenance mode, and follow the consequent instructions.

Step 4: After disabling the security firewall, visit your website and perform the actions that were previously triggering the invalid JSON error in WordPress. Check if the error persists.

If the error is resolved after disabling the firewall, it suggests that the security firewall was blocking legitimate REST API requests. This doesn’t necessarily mean that the firewall itself is faulty; it may have been triggered by a false positive.

Step 5: Once you’ve confirmed that the security firewall was the source of the problem, re-enable it according to the plugin’s instructions. You need to keep your website secure.

But, when activating the plugin, make sure to configure it properly to prevent false positives. That ensures your security firewall doesn’t block essential requests, review and configure the firewall settings carefully.

Turn on the Debug in the WordPress

Enabling debugging allows you to capture error messages and warnings, which can provide insights into the root cause of the invalid JSON response in WordPress. Here’s how you can fix the invalid JSON error in WordPress by turning on the debugging.

Step 1: Log into the WordPress admin dashboard.

Step 2: Access the wp-config.php file located in the root directory, through the FTP client or hosting file manager.

Step 3: After locating the wp-config.php file, open and edit it through a text or code editor like Notepad or Visual Studio Code.

Step 4: Now, locate the section containing WordPress database settings in the wp-config.php, and add the following code excerpt.

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);

Here’s what each line does:

• WP_DEBUG: This sets debugging mode to “true.”
• WP_DEBUG_LOG: It logs debugging information to a file named “debug.log” located in the “wp-content” directory.

Step 5: Save the changes you have made to the ‘wp-config.php’ file.

After that, visit your website and repeat the actions that lead to the invalid JSON error in WordPress.

Step 6: Look for and open the “debug.log” file, i.e. the WordPress error logs, and review the content.

The entries in the debug log will provide details about what might be causing the invalid JSON  error in WordPress. Based on the debug log, you can start troubleshooting the issue. Errors and warnings in the log may point to specific themes, plugins, or server-related problems that need attention.

Step 7: Identify the cause and fix the invalid JSON error in WordPress, and then disable the debugging to prevent the indefinite growth of the debug log. For that, simply set ‘WP_DEBUG’ to ‘false’ in the ‘wp-config.php’ file.

define('WP_DEBUG', false);

After making changes based on the debug log, perform additional testing to ensure that the “Invalid JSON Error” is resolved. Although debugging in WordPress is a powerful tool for diagnosing and fixing issues, it should be performed cautiously, since it contains a lot of sensitive data.

Upload Media Files Through the Media Library

As part of the troubleshooting steps for fixing the invalid JSON error in WordPress, upload the media files through the WordPress media library.

Step 1: Log into the WordPress dashboard, go to the “Media” section, and click on “Library”.

Step 2: At the top of the Media Library page and click on the “Add New” button. Then select a media file from your computer, and upload it to your website.

Step 3: If you encounter the invalid JSON error in WordPress during or after uploading the media file, take note of the details of the error message.

Step 4: If the error occurs during the media upload process, it suggests that there may be an issue related to media handling or file processing on your server. Possible causes could include server resource limitations, incorrect file permissions, or a corrupted media file.

To fix the invalid JSON response error in WordPress, try the following:

• Check your server’s resource usage and available disk space.
• Ensure that file and folder permissions are set correctly on your server.
• Verify the integrity of the media file by uploading a different file to see if the error persists.
• Contact your hosting provider for assistance with server-related issues.

You have to understand the invalid JSON error in WordPress can be due to a variety of reasons, and the resolution will depend on it.

So if you want to accurately identify the cause behind this error, I suggest you hire professional WordPress developers. With their vast developer resources, these experts will diagnose and fix invalid JSON errors in WordPress quite effectively.

FAQs on Fixing the Invalid JSON Error in WordPress

Let’s Summarize

Dealing with an “Invalid JSON” error in WordPress can be frustrating, but most causes have straightforward fixes. It may be due to a plugin conflict, incorrect URL settings, or server misconfiguration. But methodically troubleshooting the issue will usually lead you to the solution.

Start with the simplest checks—disabling plugins, switching themes, or verifying REST API access. Then dive into deeper fixes like debugging or server configurations. Keeping WordPress core, themes, and plugins updated also helps prevent many JSON-related issues.

And if the problem still persists, connect with our WordPress experts today!!