Depending on the specifics of the project, we use one of two approaches
The project is divided into tasks, each of which the team evaluates separately, so you have the opportunity to make any additions in the course of the work. When the task is completed and you have a visible result, you pay the team (payment can take place immediately after the sprint, monthly, quarterly, etc.). – as you like). This model is ideal for MVPs or projects that may change depending on the market. Project release and testing occurs at the end of each phase.
The model assumes that the budget for the development of the entire project and its Terms of Reference are approved before the start of work and remain unchanged. Also, before the start of work, the exact calendar date of project delivery is approved, which is based on the Statement of Work. Thus, you know exactly the cost and timing of the project, but can not make changes in the course of development. Release and testing of the project occurs at the end of all work.