This is a tricky one. You might not have a particular model in mind, or you might have many. You might not be charging (at least at first) for your solution. The thing is, this is not a charitable fundraiser – you need to be able to show investors how they will see a large return on their investment. So think logically – what makes the most sense for your product? Subscription? Ads? Promoted Content? Premium Features? Analytics and Reports? Try to find the best match and then discuss a few possible future revenue streams.