How do you approach validation when the users of your product and the customers are different?

For context, I’m building a social impact start up focused on an acute problem for low-income families. We have piloted the product with no code tools and have had 20 users plus 80+ waitlist sign ups in a few weeks.

However, our customers will be businesses that benefit from the increase spend of these families at their stores. How would you go about validating the business model when you know the users want it, but not sure for customers? For early sales conversations, do you always show a prototype? Or do you just verbally pitch the product and get feedback on willingness to pay?