@josh Small correction: in the EU, the payment network is SEPA. IBAN is just the numbering system for bank accounts.
@alex Regarding "FOSS self-hosted platform", this will be the 378th time that I tell you about https://hub20.io, which started as a "payment gateway and "self-hosted Venmo for crypto", but it has since become extensible for *any* type of payment network and wouldn't take too much work to add FedNow support.
Please don't reinvent this wheel, and take a look at hub20.