Happy birthday.
Point your camera at the QR on the card. That is the whole thing.
On shop shelves, ready to give
You buy the physical card. The QR is already printed on it. Scan it, record a birthday wish, and the next person who scans hears it.
Point your camera at the QR on the card. That is the whole thing.
Pick one up in a convenience store. Every card already has its own unique QR code printed on it.
The first scan opens a recorder. Speak a wish, preview it, then save it to that card.
Whoever scans that same QR later hears the recording. No app to install.