Domains > example.com > Move domain is greyed out.
When trying to move it via CLI to a new/existing subscription the following error is shown:
# plesk bin site --move example.com -login john_doe -passwd <password>
Unable to move the domain because it shares the document root with another domain: example.com.example2.com.
exit status 1
It is one of the knows limitations of moving a domain: it is not possible to move a domain if there is already a domain with the same document root owned by the current subscription.
Change the Document Root for either one of the domains in order to Move the domain.
Go to Domains > example.com > Hosting Settings;
Note: Usually if both domains have the same Document Root it's because it has been migrated from another control panel, such as cPanel. Copy all files to the new Document Root before moving the domain.