As far as I know, this doesn’t work that way. You need to be on the Starter (free) plan for its quotas to work. A team can’t be on Starter and Professional plan at the same time. And since you have one design seat in your team, once you add FigJam files to the team, you also can edit them so you have to pay for FigJam Professional plan. Keep these FigJam files in your Drafts so you don’t get charged for them.