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.
The answer to this is always self capitalization is fastest + usually cheapest way to go.
Without more detail, no way to determine how best to direct you to design of this type of money flow.
Try searching Google for how similar products were self capitalized, or...
Get on the phone with anyone you know who understands self capitalization.
All my businesses are self capitalized.
And... I'm hooked on this approach, because of the zero wait time till first sales.
Waiting on money from anyone incurs a massive net loss in opportunity cost.
In other words, if it takes you six months to find $50K + you have to give away 75% of your business... you just lost...
6 months of sales + 75% of your business.
Better to start making sales today + keep 100% of your business.
In my experience, $50,000 only makes sense coming from friends & family. You'll burn through the cash quickly and likely won't reach a meaningful business inflection while spending that $50k. If you're just trying to get a prototype built, most angels and even accelerators will tell you to come back when you have something real and a few users/customers.
In short, they should figure out how to build it themselves or get some friends & family to pitch in to pay for the prototype to be built.