If you are using MediaWiki with the VisualEditor extension and try to create a subpage, you will probably get the error message:

Error contacting the Parsoid/RESTBase server (HTTP 404)

Resolution - cPanel Servers

If you are on a cPanel Shared Hosting or Reseller Hosting server, please contact technical support as the resolution in this KB requires our team to make some configuration changes on the server.

If you have your own cPanel server, follow these directions:

Connect to the server as the root user and run the following command, replacing the username and domain with the appropriate values.

mkdir -p /usr/local/apache/conf/userdata/std/2_4/username/domain.tld/

Create a config file - in this case, we're calling it slashes.conf.

vi /usr/local/apache/conf/userdata/std/2_4/username/domain.tld/slashes.conf

Add the following to the file:

AllowEncodedSlashes On

And then save the file.

Run the following script to rebuild the httpd config:

/scripts/rebuildhttpdconf

Restart Apache: 

/scripts/restartsrv_apache

Now you can create a subpage within MediaWiki using VisualEditor.

Resolution - Apache Servers

Edit your main Apache conf file (for RHEL-based distros, this will be in /etc/httpd/conf/httpd.conf) and add:

AllowEncodedSlashes On

Restart Apache