Hey ​@digitalfactory , thanks for reaching out in the Figma Forum!
I was able to see your support case and can see that one of our Support agents has already replied. Sharing a high-level update here as well in case it's helpful for others:
We can confirm that the unassigned Developer seat is what's generating the prorated charge on your upcoming invoice. On Organization plans, additional paid seats added during the annual term are typically billed on a prorated basis and remain available for use until the subscription renews.
More information in our Help Center article:Â Manage billing on the Organization and Enterprise plans
The Billing team is already reviewing your request. For any further updates, please continue the conversation directly through your existing support case, as they'll be best equipped to assist you from there. I’ll go ahead and close the topic here, thanks for your patience!