This is probably the key. Do you know why users aren't using the product? Have you asked them? It sounds to me like you have a market where one side has a problem, but the other side doesn't.
In that case move onto something else. Unless the side with the problem can force the other side to use your product then you don't have a viable business.
have you considered which side of the market is more important to focus on first
if you can get a lot of attendees to willingly use the app, the event organizers will follow. They might even knock down your door demanding to pay you $ for a chance to be your customer
if you get the event organizers to sign up, but the attendees don't use the app, then the event organizers will leave
so it would be best to focus on signing up attendees first? aren't they 100x more important then convincing the event organizers? just a thought.
yes that is probably a succinct way to express it