Start with the reason this custom software development usa should exist, not a list of screens. What kind of user will use it day to day, with what frequency, and what happens today? A vendor who grasps the purpose can propose an alternative that costs less; one who only sees a list of screens can only price exactly what you asked for.
Define what is included as short scenarios: who does what, and what happens next. Just as important, list what the first release deliberately excludes. An explicit list of exclusions saves more disagreement at delivery time than almost anything else in the document. Also mark which parts are firm and which may still change — the difference changes the price, and pretending everything is fixed only hurts you.
Write down the hard constraints. This means existing systems the software has to talk to, the data you already hold and its condition, security and compliance rules, expected load, which devices matter and infrastructure that is already decided. If a deadline is real, say what depends on it: a team is usually able to rearrange the plan to protect it, but only if they know it exists.
Write down what the word done means feature by feature. Clear acceptance criteria do not require formal language: a short paragraph describing the expected behaviour will do. That one addition shortens the sign-off process by a surprising margin and removes most late-stage disagreement.
One last thing, ask for a specific format. Request a task-level breakdown, the assumptions behind each number, the risks the team sees and a range rather than a single figure. Treat a wide range as useful information rather than evasion: it usually points to the part of the brief that needs work. From there clarify that area and hire react native development ask again — the next version tends to be the one worth planning around.