Hi Peter, You have created this form using the Neartial templates. You can enable the inventory for the Registration fee item and add the available seats. Login to Neartail > click on the form to open it > Edit page will be displayed > In the Edit page, click on the gear icon next to the Registration fee > Product settings page will be displayed > click Advanced > enable the inventory feature > enter the available stock and click Save. Neartail keeps track of the product orders and then automatically marks the item as sold out when the available stock becomes zero. Please try this and confirm.