They have a number of money making initiatives. As the see themselves as the "hub"[1] for your finances the biggest opportunities I think are probably outside of core lending functions.
- Partnership/Affiliate revenue by way of their "marketplace" initiatives. They get a cut of recommending services for customers. Recent examples include new utility (electricity) providers. [2] Also interest/savings accounts. [3]
- Monzo Plus - "premium" banking features such as virtual cards, metal cards, access to a curated "cheaper" market place [4]
- Monzo Business - business banking, initially focused on small - medium sized business with invoicing, payment and tax management built in [5]
- core lending as other customers have pointed out