Hi Barry,
Thanks for the KUDOS! :)
The s2Member Pro Coupons unfortunately cannot be used to offer Free Registration, so you’d need to implement a different voucher/coupon system. This has been described in Knowledge Base » Offering a Free Coupon Code (100% Discount).
The way I’d implement this functionality in your scenario would be to create a page that contains a Free Registration form that only gives access for 24 hours (see the Optional Tip under Dashboard -› s2Member® -› PayPal® Pro Forms -› Free Registration Forms).
I would also configure that Free Registration form to assign specific Custom Capabilities to that user when they sign up (perhaps even doing it dynamically basing the Custom Capability on the voucher code that was used, so each event gets its own Custom Capability). Then, you’d create pages/posts for that event and restrict them to that Custom Capability.
To restrict access to that page with the free registration form, I’d implement a voucher code system like the one described in the Knowledge Base article above. For greater security, you may want to implement a system of dating voucher codes, allowing them to only be used up until a specific date (for example, within 5 days of the event where you handed out the code).