Updating failed. The response is not a valid JSON response.

The issue is not from Gutentor but sometimes while using Gutenberg the following issues may come.

Updating failed. Error message: The response is not a valid JSON response.

Publishing failed. Error message: The response is not a valid JSON response.

Quick Solutions:

  • Go to Settings => Permalinks. Select Post name and save.
  • If it is already selected, you can just click Save Changes again.
  • Make sure Rest API is working fine on your website.
  • After that try to save your post/page again

Most of the time the Quick Solutions fix the issue.

Next Solutions:

  • Make sure your installation meets the server requirement.
  • Deactivate plugin one by one and try to save the post, if the plugin is causing this, you will find it.
  • Delete revision post using any of the delete revision plugins.

Check if the issues is fixed.

Final Solutions:

  • From your Cpanel file manager or FTP, goto WordPress installation and write following code on wp-config.php, see WP DEBUG
    define( 'WP_DEBUG', true );
    define( 'WP_DEBUG_LOG', true );

    after that try to save the post and view the debug.log log file inside the /wp-content/ folder. There should be an error. Try to solve that.

  • From your Cpanel file manager or FTP, goto WordPress installation and delete the .htaccess file. After that from WordPress Dahbboard to Settings => Permalinks. Select Post name and save.