These functions are available on Monzo App at the moment, but they’re hidden in a very inconvenient place (different place to main app starting place), the triggering buttons cannot be moved (for example, to the start page next to your accounts), and approving / rejecting payments is buggy (if you click approve, it takes you on several different pages).
See MobilePay App in the Nordics (Finland, Sweden, Denmark and Norway) for how easy this should be. This app is overtaking all payments between people in the Nordics and is considered gold standard. If Monzo has this, it would be perfect