It wouldn’t need a separate app if, for instance, a standard QR payment format way created. If you just want a link to a website to pay, then naturally that would be less secure, but you could always put the URL below the QR code for redundancy (QR would only save time typing then).
A tea bag floats though. It’s better to use the traditional balls or anything else metal that will make the tea sink so it soaks better. Alternatively, there are ceramic teapots that keep the tea leaves below the water level.