You literally enter an IBAN and the transfer will appear in the other account the next day. And if you need the money in the target account immediately (within 10 seconds) you can do it, too, by checking a checkbox for a small fee and that fee will drop to ZERO across the EU in October 2025.
Edit: Do you mean that the speed of the transfers was the problem?
Zelle, previously known as clearXchange, and whatever else, but if you had an account at one of the bigger bank, it has long been trivial to send money to each other.
https://en.wikipedia.org/wiki/Zelle
> In April 2011, the clearXchange service was launched. It was originally owned and operated by Bank of America, JPMorgan Chase, and Wells Fargo.[6][7] The service offered person-to-person (P2P), business-to-consumer (B2C), and government-to-consumer (G2C) payments.[8]