When a WordPress editor shows the message “Updating failed. The response is not a valid JSON response”, it usually means the site tried to save or publish content but did not receive the expected response from the server. This is common in the block editor and can happen after a plugin update, permalink change, hosting issue, security rule, or REST API conflict.
TLDR: This WordPress error is usually connected to the REST API, permalinks, mixed HTTP/HTTPS settings, plugins, themes, or server security rules. The quickest fixes are to resave permalinks, check the site URL, disable conflicting plugins, and confirm that the REST API is working. If the issue continues, the site owner should review server logs, firewall settings, and hosting configuration.
What the Error Means
WordPress uses the REST API to communicate between the editor and the server. When a user clicks Update, Publish, or Save Draft, WordPress expects a valid JSON response. JSON is a structured data format that WordPress can read and process.
If the response is broken, blocked, redirected, or replaced by an HTML error page, WordPress cannot understand it. As a result, it displays the message: “Updating failed. The response is not a valid JSON response.”
This does not always mean the post is lost. In many cases, the content remains in the editor or can be restored from revisions. However, the underlying cause should be fixed to prevent future publishing problems.
1. Resave WordPress Permalinks
The first and simplest fix is to refresh the permalink structure. Incorrect or outdated rewrite rules can prevent WordPress REST API requests from reaching the right endpoint.
- In the WordPress dashboard, go to Settings > Permalinks.
- Do not change anything unless necessary.
- Click Save Changes.
- Return to the post or page and try updating it again.
This action regenerates rewrite rules and often fixes the error immediately. If the site uses a custom permalink structure, the owner should make sure it is valid and does not contain unusual characters.
2. Check the Site URL Settings
A mismatch between the WordPress Address and Site Address can cause invalid responses. This is especially common after moving a site, enabling SSL, or changing domains.
The site owner should go to Settings > General and confirm that both fields are correct:
- WordPress Address (URL)
- Site Address (URL)
If the website uses HTTPS, both URLs should usually begin with https://. A mix of HTTP and HTTPS may trigger redirects or blocked requests, which can break the JSON response.
3. Fix Mixed Content and SSL Issues
SSL problems are another frequent cause. If parts of the site load over HTTP while the editor communicates over HTTPS, the browser or server may block requests.
The site owner should verify that the SSL certificate is valid and active. They can also check whether the WordPress dashboard, posts, pages, and media files all load securely. If the site recently moved to HTTPS, it may need a proper redirect from HTTP to HTTPS.
In some cases, updating the database URLs from HTTP to HTTPS may be necessary. This should be done carefully, preferably with a trusted search-and-replace tool or by a developer, because incorrect changes can affect serialized data.
4. Test the REST API
Since the block editor depends on the REST API, testing it can help identify the problem. A simple way to check is to visit:
https://example.com/wp-json/
The domain should be replaced with the actual website address. If the REST API works, the page should display structured JSON data. If it shows a security message, 404 page, 403 forbidden page, login screen, or server error, something is blocking or modifying the response.
Common causes include security plugins, firewall rules, server restrictions, or incorrect rewrite rules. Once the owner knows the REST API is not responding correctly, troubleshooting becomes more focused.
5. Disable Plugins Temporarily
Plugin conflicts are one of the most common reasons for this WordPress error. Security, caching, optimization, translation, and editor-related plugins can interfere with REST API requests.
To test this safely, the site owner can:
- Go to Plugins > Installed Plugins.
- Deactivate all non-essential plugins temporarily.
- Try updating the post again.
- If the error disappears, reactivate plugins one by one.
- Test the editor after each activation to find the conflicting plugin.
If the site is live and receives traffic, it is better to perform this test on a staging site. That avoids disrupting visitors or breaking important front-end features.
6. Switch to a Default Theme
A theme can also cause an invalid JSON response if it includes custom editor features, REST API modifications, or faulty functions. To test for a theme conflict, the owner can temporarily switch to a default WordPress theme such as Twenty Twenty-Four or another current default theme.
If the post updates successfully after switching themes, the active theme is likely causing the issue. The owner should update the theme, check its functions file, or contact the theme developer for support.
7. Check Security Plugins and Firewalls
Security tools sometimes block REST API requests because they mistake them for suspicious activity. Web application firewalls, bot protection systems, and server-level security rules can all interfere.
The site owner should review settings related to:
- REST API access
- XML-RPC and API restrictions
- Firewall blocking rules
- Login protection
- Country or IP blocking
If a security plugin is responsible, the solution is usually to whitelist REST API routes or adjust firewall sensitivity. The specific route often begins with /wp-json/wp/v2/.
8. Clear Caches
Caching can sometimes serve an old, redirected, or invalid response to the editor. The site owner should clear all available caches, including:
- WordPress caching plugin cache
- Server cache
- CDN cache
- Browser cache
- Object cache, if used
After clearing caches, the editor should be reloaded in a fresh browser tab. If the site uses a CDN, its security and page rules should also be checked to ensure REST API requests are not cached or challenged.
9. Review the .htaccess File
On Apache servers, WordPress uses the .htaccess file to manage permalinks. If this file is damaged, missing, or incorrectly edited, REST API requests may fail.
A standard WordPress .htaccess file usually contains rewrite rules between WordPress comments. The owner can regenerate it by resaving permalinks. If manual editing is required, a backup should be created first.
Users on Nginx servers will not rely on .htaccess in the same way. Instead, they may need to ask their hosting provider to check the server configuration.
10. Increase PHP Memory and Check Server Errors
If the server runs out of memory or encounters a PHP fatal error while saving content, it may return an invalid response. The editor then displays the JSON error instead of a more specific message.
The site owner should check the hosting control panel, error logs, or WordPress debug log. Common signs include PHP memory errors, plugin fatal errors, timeout messages, or permission issues.
Increasing the PHP memory limit may help, but it should not be used as the only fix if a plugin or theme is generating repeated errors. The real cause should still be identified.
11. Use the Classic Editor as a Temporary Workaround
If urgent content must be published, the Classic Editor can sometimes bypass the issue temporarily because it does not rely on the block editor in the same way. However, this should only be considered a short-term workaround, not a permanent fix.
The JSON response error usually points to a deeper configuration or compatibility problem. The site owner should still resolve the REST API, plugin, theme, or server issue.
FAQ
What causes the “not a valid JSON response” error in WordPress?
It is usually caused by REST API problems, permalink issues, SSL mismatches, plugin conflicts, theme errors, firewall rules, caching problems, or server misconfiguration.
Is the content lost when this error appears?
Not usually. The content may still be visible in the editor, saved as an autosave, or available through post revisions. The user should avoid closing the tab before copying important content.
Why does resaving permalinks fix the issue?
Resaving permalinks refreshes WordPress rewrite rules. If those rules are broken, WordPress may not route REST API requests correctly.
Can a security plugin block the WordPress REST API?
Yes. Some security plugins or firewalls block REST API endpoints. Adjusting the settings or whitelisting /wp-json/ routes can resolve the issue.
Should a site owner contact hosting support?
Yes, if basic fixes do not work. Hosting support can check server logs, firewall rules, SSL configuration, permissions, and REST API access at the server level.