When you are ready to launch a new marketing campaign or publish an urgent announcement, clicking “Publish” should be seamless. Instead, hitting the button freezes the Block Editor (Gutenberg) and returns a frustrating banner: "Publishing failed. Error message: The response is not a valid JSON response." or a direct 403 Forbidden warning.
When you check your browser console or backend security logs, you will find a strict REST API connection failure referencing the wp-json pathway. Standard forum advice usually suggests “re-saving your permalinks” or “switching to the Classic Editor.” This is an incomplete workaround. This error indicates that your site’s automated asynchronous background handshake is being aggressively blocked by server-level firewalls or security plugin rules (like Wordfence) that mistake Gutenberg’s save routines for a malicious script attack.
Below is the technical reason why this security block triggers and the exact methods to whitelist your editor REST endpoints and restore publishing access instantly.
The Error Snippet
When the block editor fails to update a page layout or handle a post submission, opening your browser’s Developer Tools (Console Tab) will expose this failing connection:
Plaintext
POST https://techbic.site/wp-json/wp/v2/posts/1024?_locale=user 403 (Forbidden)
OR
REST API Exception: wp_json endpoint is missing or blocked by security policy.
Why This Happens (The Real Technical Cause)
The modern WordPress Block Editor does not use traditional PHP page submits to save content. Instead, it relies entirely on the WordPress REST API. Every character you type, layout container you build, or image you insert is continually packaged and pushed via background asynchronous POST requests to endpoints like /wp-json/wp/v2/posts/.
This publishing freeze occurs due to a Security Rule False Positive or a Permalinking Rewrite Disconnect.
When you click “Publish,” Gutenberg sends a massive block of raw HTML data strings (which contain layout parameters, script tags, and shortcode structures) inside a JSON payload. Security application filters like Wordfence (WAF), Cloudflare Web Application Firewalls, or server modules like mod_security analyze this incoming string traffic.
If a paragraph contains sample code snippets, strict layout stylings, or nested link configurations, the security layer mistakenly flags the payload as a potential Cross-Site Scripting (XSS) or code injection attempt. The firewall instantly intercepts the loop and returns a hard 403 Forbidden response. Because Gutenberg receives an HTML firewall block page back instead of a clean JSON status confirmation, the script panics and locks the editor screen.
How to Fix It Safely (Step-by-Step Solutions)
Follow these direct technical steps to drop your security layers into learning mode and repair broken REST endpoint routing layers.
Fix 1: Place Wordfence WAF into “Learning Mode” to Whitelist Gutenberg
If you run Wordfence and see a block screen or a 403 error in your log files, you must train the firewall to recognize your custom editor blocks instead of completely dismantling your security shield.
1.Access your backend security controls:
Step 2.1.
Log into your WordPress administrative dashboard and navigate to the sidebar menu item Wordfence -> Firewall.
2.Modify the Web Application Firewall status:
Step 2.2.
Locate the option dropdown labeled Web Application Firewall Status. Change the selection from “Enabled and Protecting” to “Learning Mode”. Click Save Changes.
3.Execute the publishing action to record parameters:
Step 2.3.
Navigate back to your broken post or landing page and click Publish or Save Draft. The layout will now save successfully because the firewall is actively analyzing the request data rather than blocking it.
4.Lock down the firewall rules permanently:
Step 2.4.
Go back to the Wordfence Firewall configurations page. You will see a newly generated whitelist line tracking the exact /wp-json/ route that was blocked. Switch the status back to “Enabled and Protecting” and save. The firewall is now fully secure while completely allowing your block layouts to publish smoothly moving forward.
Fix 2: Repair .htaccess Rewrite Rules for the wp-json Router
If your security logs are clean but the system claims the wp_json endpoint is entirely missing, your server’s routing path mapper is broken. This frequently happens when changing hosting providers or altering domain structures.
Open your site’s root directory via FTP or File Manager, open your .htaccess file, and ensure the core WordPress routing block is properly reinstated at the bottom:
Apache
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
# Route all requests cleanly through index.php if they don't point to a real file or folder
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
(This ensures that whenever Gutenberg queries /wp-json/, Apache cleanly redirects the path string into the core WordPress controller instead of returning an empty 404 or 403 error page).