Moving a workspace from an subscription to another subscription can be helpful for example to make sure you pay only once for the same person across workspaces, or to keep all of your workspaces under one single billing.
To proceed you need to:
1 - be an admin of the workspace you want to move
2 - be a manager of the source subscription
3 - be a manager of the target subscription
From the workspace Settings panel select the target subscription you want the workspace to be moved to:
N.B.: New people who are not already known on the target subscription will automatically get billed on this subscription.