WordPress is preferred by millions of sites worldwide due to its ease of use and flexible infrastructure. However, users may occasionally encounter the error "Publishing failed. Response is not a valid JSON response." In this article, we will explain the causes of this error, solutions, and sample steps step by step.

Quick Solution Suggestion

Go to the Settings > Permalinks page and press the Save Changes button. Saving, even if you don't change anything, often fixes this problem.

Why Does This Error Occur?

The JSON error in WordPress usually stems from REST API issues. The most common reasons are:

Incorrect permalink settings
Plugin or theme conflict
Server-side PHP setting issues
SSL certificate problems or HTTP/HTTPS confusion
CDN or firewall preventions

Detailed Solutions and Sample Applications

1. Re-save Permalink Settings

Steps:

Log in to the WordPress Admin Panel.
Go to Settings > Permalinks.
Click the Save Changes button without making any changes.

Example: If you are using the /%postname%/ structure, just save it.

2. Check Plugins and Theme

Disable all plugins.
If the problem is resolved, find the problematic plugin by activating the plugins one by one.
Check if this problem occurs in custom themes by changing the theme.

Note: Especially "security" plugins may block REST API access.

3. Fix SSL Certificate and HTTPS Settings

Make sure site URLs start with HTTPS.
In Settings > General, WordPress and Site URL should be HTTPS.
Make sure your SSL certificate is valid and active.

4. Optimize Server Configuration

Make the PHP version at least 7.4 or 8.0.
Set the memory_limit value to 256M or more.
Have Mod_Security settings checked (it should not block REST API).

5. Check CDN, Firewall and Reverse Proxy Settings

Be careful not to block REST API paths in services such as Cloudflare.
Incoming POST requests (wp-json) should not be restricted by the firewall.

Example: If you are using Cloudflare, you can define a Page Rule for the WordPress REST API.

Extra Solutions

Add Debug Codes to WP-Config Settings

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

These settings create detailed error logs in the wp-content/debug.log file.

Track Errors from Browser Console

Open Chrome developer tools (F12).
Go to the Network tab and look at wp-json requests.
If the response is empty or incorrect, you can see the details here.

Frequently Asked Questions (FAQ)

Q: Does this error only occur when saving a specific post? A: There is probably a JSON parse error in the content of that post (e.g. incorrect code blocks).

Q: Can the problem be caused by the hosting company? A: Yes. Firewall settings, mod_security rules, or old PHP versions on the hosting may cause this problem.

Q: SSL installation was done recently, why does the error persist? A: You may have forgotten to update the WordPress site URL settings with HTTPS.

Conclusion

The error "Publishing failed. Response is not a valid JSON response." can be frustrating for WordPress developers and site administrators, but it is not unsolvable. By following the steps in this guide, you can easily fix 95% of the problems.

If the problem persists, getting professional support and performing complete WordPress maintenance will be the most accurate choice in the long run.

Recommendation: Always using a strong hosting infrastructure for WordPress (such as https://www.ekasunucu.com/paylasimli-hosting, https://www.ekasunucu.com/vps) prevents such errors.

Did you find it helpful? You can send us your questions in the comments or consult us for professional support!