If you outsource part of your software development project to a third-party, you may think that the best type of contract to sign is Fixed-Price: you set the scope, they promise the time and price, they deliver, you check the quality, and you pay. It sounds right, but in reality, it'll be a disaster. Instead, always sign Time&Material contracts: you tell them how much resources you need, they give you a quote per hour, you manage them, they work for you, you pay every month. This is much more effective.
The video is here: https://youtu.be/xUALewcix44