Updating failed. The response is not a valid JSON response

The “Updating failed. The response is not a valid JSON response” error in WordPress typically occurs due to issues with the REST API, which WordPress uses to handle AJAX requests, including saving posts, pages, or updates. Here are some common causes and troubleshooting steps:

1. Permalinks Issue

• Solution: Go to Settings > Permalinks and simply click Save Changes without altering anything. This refreshes the permalink structure and can often resolve JSON-related errors.

2. SSL or Mixed Content Issues

• If your site is using SSL (https) and there is a mix of HTTP and HTTPS requests, WordPress might block the request, leading to a JSON response error.
• Solution:
  • Ensure your WordPress URL and Site URL under Settings > General are set to https://.
  • Consider installing the Really Simple SSL plugin to handle SSL-related issues.

3. REST API Blocked

• Sometimes the REST API is blocked by a security plugin or web host configuration.
• Solution:
  • Disable security plugins temporarily (like Wordfence or Sucuri) to see if the issue resolves.
  • Check if your hosting or a firewall (e.g., Cloudflare) is blocking REST API requests.

4. ModSecurity or Web Application Firewall (WAF)

• If you have a web application firewall or ModSecurity enabled on your server, it might block the REST API request.
• Solution: Disable the firewall temporarily or check with your host to ensure it’s not blocking legitimate requests.

5. PHP and Memory Issues

• Insufficient PHP memory or outdated PHP version could be causing the issue.
• Solution: Ensure your site is running on PHP 7.4 or later. Increase PHP memory limit by adding this to your wp-config.php:
  

define('WP_MEMORY_LIMIT', '256M');

6. Gutenberg/Block Editor Conflict

• The block editor (Gutenberg) might have conflicts with other plugins or themes.
• Solution: Disable all plugins except core ones and see if the issue persists. If it stops, enable the plugins one by one to find the culprit.

7. .htaccess or NGINX Configuration

• If you’re using NGINX or have custom rules in .htaccess, there could be conflicts.
• Solution: Check for any rules in .htaccess or NGINX configuration that might be blocking the REST API requests.

8. Permitted HTTP Methods

• Your server may not be allowing the required HTTP methods (like POST or PUT).
• Solution: Ensure that the methods POST, GET, PUT, and DELETE are allowed on your server.