The full answer
At the start, the most useful thing you can bring is context: who the users are, what problem the product solves, how you will measure success and any deadlines that matter. Existing research, sketches, competitor examples or documents help but are not required.
During the project, we need a product owner on your side who can attend sprint demos, answer questions and make decisions. Delayed feedback is one of the most common reasons projects slip, so a responsive decision-maker matters more than a long requirements document.
Practical access matters too: API credentials and documentation for systems we integrate with, test accounts, brand assets, copy and content, and access to developer accounts such as the Apple App Store, Google Play and your chosen cloud provider.
If you lack some of these, such as brand assets or written content, we can advise on options during discovery. Our engineering lead will share a checklist at kick-off so nothing is missed.
Time is the other ingredient. We ask product owners to set aside time for each sprint demo and for answering questions during the sprint, which usually saves far more time than it costs.