A subscription is an instance of plan assigned to the reseller account or customer account. It is like creating the new cPanel account in WHM and assigning the package to the cPanel account. Subscription is otherwise considered as an agreement to consume the resource and services on Plesk. And the subscription is linked to the main/primary domain that the specific account created.
To display a list of all subscriptions on the source server (the user “root” credentials are used to access the source server), use the command
plesk bin migrate.exe --list-subscriptions -host 192.168.1.100 -password mypassword
(or)
plesk bin migrate.exe -ls -host 192.168.1.100 -login root -password mypassword