How do I ask for pre-payment during problem validation?

I'm working on validating a problem right now. I'm going about it by finding people and talking to them on a Meet call / phone call. If I build it, this solution would be for the company but not necessarily a team buy - (ie) it can potentially be bought by the individuals without much approvals.

My questions are:

1. how do I go about asking interested folks to put up pre-payment for this solution?
2. Have there been any approaches that worked to get pre-payment, and have there been any that backfired?
3. Would you always count reluctance to put up pre-payment as invalidation of the problem being important?

Since I have not done sales till now, apologies if these questions are too trivial.

Big thanks :)