Open with the business problem, not your preferred technology. Which people will use it day to day, with what frequency, and how is the job done today? An experienced team who grasps the purpose will suggest a simpler way to reach it; someone handed only a feature list prices exactly what you asked for.
Define what is included as concrete flows: what the user does and what the system does in response. Every bit as useful, write down what you are not building. An explicit exclusion list removes more friction during acceptance than almost anything else in the document. Also mark which parts are firm and which may still change — estimators price uncertainty, and saas custom development hiding it helps nobody.
Set out your constraints. The list covers systems you must integrate with, the data you have and where it lives, security and compliance rules, expected load, supported browsers or aws development company devices and infrastructure that is already decided. If there is a hard date, explain what drives it: a good team can often rearrange the plan to meet it, igaming platform development but only if they know it exists.
Say what completion means feature by feature. Clear acceptance criteria do not need any formal notation: a plain-language note setting out what must be true when the feature works is enough. That one addition shortens acceptance testing considerably and closes off most late-stage disagreement.
To close, state what you want in the response. Ask for a breakdown by feature or module, a written list of assumptions, the main risks and a low number and a high number. Read a wide range as useful information rather than evasion: it usually points to exactly which requirement is unclear. Then rewrite that part and request a revised number — the next version will be the one worth planning around.