> He didn’t even try the app once before presenting it to the investors

Ah ah, so classic. It just happened to a client I have (I only manage hosting for them)

<slack alert> : we have this one page down with an error, but it's the landing page of a mailing we just sent ! <me> : do you had the error when testing before launching mailing ? <client> : mmmm.....

Problem was solved by the developer in a matter of minutes, but it's always a good lesson.