I've always assumed that they make their money through mining customer data and merging it with e.g. Facebook Pixel datasets etc, but I have no evidence for this. Just seems like the 'obvious' business model for a tech-focussed bank as I assume that traditional banks have more difficulty in adapting their systems for these kind of use cases and I don't see how they could offer so much for free based on small monthly fees from a handful of people.

That said, they're also looking more and more like they might become the Robinhood of Europe, which brings its own revenue models.