On some servers (shared hosts in particular), you may find that payment gateways are not visible in the back end.
This can happen if system.reflection fails due to the Application User account for the web site not having modify permissions for the plugins folder. If you have a panel that lets you set permissions, you can apply this to the plugins folder yourself. Otherwise, contact the host's support team and ask them to apply these permissions.
Once the folder has modify permission, the gateways should be visible.