I have wanted this for a long time. You used to be able to add notes to inbound payments on iOS, but we lost it when the transaction screen was redesigned. After all the focus on bringing Android up to parity with iOS, how about bringing iOS up to parity with Android for this feature? It’s a really irritating omission.
I submitted this request through COops in the app and they said they would pass it on to engineering. Maybe others should as well so they can see the demand for it.