Validating willingness to pay is a step that's easily overlooked. Your goal here is to get users to commit to buying your product. At the very least, you need them to express a strong interest in it. Willingness to pay is the cornerstone of the fabled product/market fit.

There are many ways to validate willingness to pay, but one of the big challenges is that we can't necessarily trust people's words. We all know those people who say "of course, I'd totally do that" but who then drop out when the time comes to commit. As far as possible, we want to get people to put money behind their words.