This error happens when you are trying to add an addon domain, or parked domain, within your cPanel management control panel.
If you are trying to add a new website, via an addon domain, and you have already used the domain in configuration elsewhere, please first remove it from the alternative configuration. For example, you may have created an addon domain in one account, whilst you are trying to create a new account through
WHM, or similar.
This can also mean that:
If removing the alternative config does not work, please contact support.