S茅bastien G. yeah, unfortunately this would likely not happen. You'd have to have a paid workspace plan in order to transfer the site. The destination workspace however does not need to have a workspace plan to receive it.
So the way that this has worked in other platforms is - you pay to build the site, once built, client pays, you create their Relume workspace, transfer, then hand over the credentials and they don't have to do anything else but login and use their website.