Poland's national postal service runs for a few years now the Internet-based postal platform Envelo, where you can send and receive personal correspondence and official letters, postal cards. Envelo allows their customers to customize and print, use postal stamps in same prices as physical ones, from home. The stamps come with small graphic, 12-digit code and data matrix code that contains all necessary information.

https://www.envelo.pl/znaczki-pocztowe/ (in Polish)

Tho, I like Sweden solution - it's way much simple; it seems they're using same 12-digit codes

They want the queen. The old stamp. Not a code I guess is the point.