I have spoken to product managers who would use the tool in lieu of their current, manual process. Of course, this is not airtight validation (see e.g. The Mom Test), but it's a start.
I have spoken to people who agreed to pay and to be sent an invoice for an existing product which they have seen a demo of live and which they loved, and did not pay when they when the invoice was sent.
I'm not saying it is not a start, but maybe we could validate further? As in, dollars in the bank account? Just a little more.