Here in Portugal we have MB Way which is handled on a separate network. I understand that it might interoperate with Bancomat (Italy) and Bizum (Spain) also just since November, but I haven’t tried yet. Almost everybody in Portugal (except non-integrating expats) seem to use it, though there are spots here and there that refuse for reasons that are unclear to me.

Well, it can be self-hosted

It is probably Chinese junk, but I’m using a set of cudy m3000 WiFi6 mesh devices that run openwrt. Could be worth looking into. They are about as cheap as I’ve seen. There should be WiFi7 versions out nowish /soon.

Wow, that looks almost exactly like my dog. Except less furry.