>> There's no paper work

No written agreement & they are sending you cash! Wow.

> The problem is that this shouldn't have been so painful for me in the first place

Startups are incredibly painful, especially at the early stage. There are always exceptions, but lots of red flags to what you've described. Most importantly it doesn't sound like your team is committed... But it also seems like they lack the relevant competency in Sales, Product or Startups. You might learn a lot by going down the path you're on, but it sounds like you're going to be learning by running through walls so I would expect it to hurt.