Summary
The most important thing in app development is not advertising or even a unique trading app. The main thing is the team to whom you entrust your idea and which will finalize and implement the idea with high quality. What is needed for that:
choose a qualified team;
fill out a detailed brief with all your wishes;
conduct a business audit of existing applications on the market (your competitors);
agree on the terms of reference with the stages of work, deadlines and budget;
give feedback on a regular basis.
Choose the best!