My wife and I did something a little similar. I built out our RSVP system on a web app, but we still printed actual invitations pointing people to go to our website, with a unique handwritten code on each one.
You can check out the code here if interested. It also includes the wedding info site as part of it, so there is a bit of cruft, but I'm sure you could repurpose it if you dug into it deep enough: https://github.com/mvarrieur/vovarrieur-dot-com
You can check out the code here if interested. It also includes the wedding info site as part of it, so there is a bit of cruft, but I'm sure you could repurpose it if you dug into it deep enough: https://github.com/mvarrieur/vovarrieur-dot-com