Having an html tag, and even a browser that interprets it and connects to grandma's saved credit card is not the problem. But where does the money go to? It has

Having an html tag, and even a browser that interprets it and connects to grandma's saved credit card is not the problem. But where does the money go to? It has to be a central body that holds all accounts and the page can specify their wallet id in another tag. How do you create that in the spirit of the open web?