Get their honest take on what sucks about their current solution/process. Ask for their expertise.
Build the thing that emerges from the 20 interviews. Not the thing they ask for, but the thing they truly need.
Craft a solid pitch from the common themes of the 20 interviews, focused on being a painkiller, not a vitamin.
Go to the place where you found those initial 20, except this time, talk about the thing you made. Not in a salesy way.
If people 1. Aren't interested; 2. Aren't converting to customers, then the thing that was built didn't properly address the pain