Updating Failed: The Response Is Not a Valid JSON Response

 

If you have ever worked with WordPress or other web platforms that rely heavily on AJAX calls and REST APIs, you might have encountered the frustrating error message:

“Updating failed: The response is not a valid JSON response.”

This error usually appears when trying to update posts, pages, or settings in the WordPress block editor (Gutenberg), and it can be tricky to diagnose and fix. This article will explore what this error means, why it happens, and how to troubleshoot and resolve it.

What Does This Error Mean?

At its core, this error means that your browser sent a request to the server (usually via the REST API), expecting a response formatted in JSON (JavaScript Object Notation), but the response received was either empty, corrupted, or not JSON at all.

In WordPress, the block editor relies on REST API calls to save and update content asynchronously without reloading the page. When the server response is not valid JSON, WordPress cannot process the response, and the update fails with this message.

Common Causes of the Error

1. Server-Side Issues

  • PHP Errors or Warnings: If your server outputs PHP errors or warnings during the JSON response, it will corrupt the JSON format.

  • Timeouts or Memory Limits: If the server runs out of memory or times out, the response may be incomplete or empty.

  • ModSecurity or Firewall Blocking REST API: Some security modules or firewalls may block REST API calls, returning an HTML error page instead of JSON.

  • Permalink or .htaccess Issues: Misconfigured rewrite rules or permalinks can cause REST API endpoints to fail.

2. Plugin or Theme Conflicts

  • Plugins or themes may enqueue scripts or filters that interfere with REST API responses.

  • Some plugins may modify REST API responses incorrectly.

  • Themes or plugins generating unexpected output can break JSON formatting.

3. SSL or Mixed Content Problems

  • If your site uses HTTPS but has insecure resources or an invalid SSL certificate, REST API calls may fail.

  • Mixed content errors can block API requests.

4. Incorrect Site URL or WordPress Address

  • If the WordPress Address (URL) and Site Address (URL) settings do not match the actual domain or protocol, REST API requests might be redirected or fail.

5. Browser or Caching Issues

  • Browser extensions or aggressive caching can sometimes interfere with requests.

  • Server-side caching plugins may cache invalid responses.

How to Fix the “Response Is Not a Valid JSON Response” Error

1. Check for PHP Errors

Enable debugging by adding these lines to your wp-config.php file:

php
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

Then, check the wp-content/debug.log file for errors that occur during update attempts. Fix any errors found.

2. Check Permalinks and .htaccess

  • Go to Settings > Permalinks in your WordPress dashboard and click “Save Changes” to flush rewrite rules.

  • Verify your .htaccess file contains the correct WordPress rules:

apache
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

3. Disable Plugins and Switch to Default Theme

  • Temporarily deactivate all plugins and switch to a default theme (e.g., Twenty Twenty-Three).

  • Try updating again. If it works, reactivate plugins one by one to find the culprit.

4. Check SSL Configuration

  • Verify your SSL certificate is valid.

  • Use tools like Why No Padlock? to find mixed content issues.

  • Make sure WordPress Address and Site Address use https:// if SSL is enabled.

5. Inspect REST API Response

  • Open browser Developer Tools (F12) > Network tab.

  • Attempt to update a post and look for the API request (usually under /wp-json/).

  • Inspect the response. If it’s an HTML page, error, or empty, that’s the issue source.

  • This insight helps in narrowing down server or plugin causes.

6. Check Server Security Settings

  • Contact your hosting provider to verify if ModSecurity or firewall rules block REST API requests.

  • Whitelist your site’s API endpoints if necessary.

7. Clear Cache

  • Clear any server-side, CDN, or browser caches.

  • If using caching plugins, purge caches and disable them temporarily.

Summary

The “Updating failed: The response is not a valid JSON response” error is a common but solvable issue that arises when the WordPress REST API returns invalid or corrupted JSON. Causes range from server misconfigurations and plugin conflicts to SSL and caching problems.

By methodically checking error logs, permalinks, plugins, themes, and server settings, you can identify the root cause and restore smooth editing functionality.

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