1) The recipient needs to download the app and sign up. How does the Payor know whether the recipient has Zelle app or not

2) Even with the app, there are only about 50-100 banks that allow Zelle transfers. If someone's bank does not offer Zelle they are directed to enter their Debit Card number using "Push to Card" to receive the funds. While the funds land up in the bank account instantly either way, some Debit Cards have limitations and will not be enabled to receive funds

3) Zelle is essentially a "messaging layer" i.e. the actual settlement happens overnight using ACH rails. As a result the sending as well as the receiving bank are taking some risk in terms of allow the recipient to withdraw money when the underlying settlement hasn't happened. If the settlement fails the receiver's bank will need to claw bank the money from the receiver As a result there are some really low limits on daily transfers i.e. between 1-2K/day for most banks

4) Above all Zelle (like most other payment rails ) is a push system i.e. one can push money using Zelle. One may not pull money using Zelle