Start with the reason this software should exist, not a feature list. Which people will use it day to day, how often, and symfony development outsourcing how is the job done today? An estimator who knows what you are trying to achieve can propose a cheaper route to it; someone handed only a list of screens can only price exactly what you asked for.
Describe the scope as user stories or scenarios: a walk through each important path. Just as important, write down what is out of scope. An explicit list of exclusions removes more disagreement later than any other single page. Mark too which decisions are settled and laravel vs node js which is better are still under discussion — estimators price uncertainty, and machine learning development company pretending everything is fixed helps nobody.
Write down the hard constraints. This means the platforms and blockchain consulting services involved, the data you have and where it lives, compliance requirements, traffic expectations, target platforms and any technology you are committed to. If a deadline is real, explain what drives it: a good team is usually able to resequence the work to meet it, but not if the date is a secret.
Write down what completion means feature by feature. Clear acceptance criteria do not require any formal notation: a short list describing what a user should be able to do is enough. This one section reduces the review at the end dramatically and eliminates most late-stage disagreement.
One last thing, ask for a specific format. Request an itemised estimate, the assumptions behind each number, whatever the team considers risky and a low number and a high number. Read a wide range as information, not evasion: it tells you the part of the brief that needs work. At that point rewrite that part and ask again — the second estimate tends to be much more reliable.