Zelle, from my understanding, is a “protocol” – many banks support it in their own apps. (Scare quotes because I’m not entirely sure it’s a proper well-defined protocol.)

And there’s nothing preventing PoS from supporting individual wallet apps – see e.g. WeChat Pay / Alipay in China. (Alipay+ is also a “protocol”, i.e. other banks and wallets support it.)

What I mean by protocol is that there is an RFC or equivalent and anyone who implements the spec and has a bank account can then talk to their bank using the standardized protocol. If that exists for Zelle then where's the spec?

I’ve searched for ‘zelle spec’ and came across this line:

> Zelle® is available in over 2,400 banking and credit union apps.

so I’m pretty sure there is a spec because there is no way in hell this many banks are using ad-hoc protocols to talk to each other and/or a centralized system. But yeah, I don’t see anything published.

Chances are it’s something ISO 20022-ish. (Either that or an Excel spreadsheet.) Speaking of which...

> and has a bank account can then talk to their bank using the standardized protocol

...if you’re a big enough business, you probably can also speak ISO 20022 to your bank. If you want it on your personal account however, well, that makes two of us, but from practical standpoint what I care more about is that I can punch in an account number and send money near instantly, which Zelle seems to provide in the US (but I have to make do with whatever Wise provides, probably regular ACH judging by speeds).

https://api.payments.jackhenry.com/docs/zelle/overview/ Is a white label api that you, as a bank, can implement/hit. Just like your local small business vendor can choose to also take Venmo and CashApp, they can also choose to take Zelle. I've bought a burrito with Zelle before.