I bought a CMS plan for a client and wants to transfer it to his workspace.
I found out that I have to downgrade the siteplan before I initiate the transfer. Can I use the siteplan and transfer it to another project in the same workspace (my workspace) ?
Yep, the siteplan is in your workspace, so you’ve paid for it.
In this case you might have the client setup a new plan in their own workspace and then refund them the prorated difference.