If you are seeing a 404 with /validatecontractkey, please verify the plugin is installed in the primary domain or a primary subdomain. It seems that our plugin does not currently like subfolders. If you installed our plugin in a WordPress subfolder then our plugin routes may not work. We have found if you create a subdomain and point it to the subfolder ten the plugin reads the route correctly.
If you cannot point the plugin to a "primary" domain, you may just be able to install it on it's own subdomain with just the plugin. We have seen this work in the past.
For now, we are trying to resolve this issue so that subfolder are not an issue, but for now this workaround has been tested.