Sounds like some great progress, especially since there's been interaction with potential customers.
Frankly, the best route for pre-seed funding would be friends and family. The team will learn how to develop a pitch and give that pitch in a somewhat "safer" environment. Plus, after they land the investments, they'll be able to point to fundraising success when they do eventually go to angel investors, who will be more receptive to a more advanced business.
Another option is getting into an accelerator program, which will ideally teach as much about building the business as it does in providing $, but that will take a separate commitment of time and resources to apply, get in and complete the program.
If you wish to discuss, send me a PM through Clarity for 15 free minutes.