At the initial stage, you can earn money via commission and subscription. You can charge a certain amount of money as a commission from professionals for every completed service. The second one is by offering some particular services only to your subscribers. So, subscribers have to pay some amount to avail the services. Lastly, you can let advertisers promote their services in your app. Charge them depending on the click-through rate. This is effective only when the plumbing app like Uber for Plumbers gets more users.