What info do you want to see in a project brief?

Hopefully, I'm in the right sub for this, but I'd assume people here are the ones I'm targeting.

My organization is planning to create an app, and we plan to outsource the development. I'm currently writing the terms of reference/project brief to invite companies to propose/apply. I'm sure that most of the details will be ironed out in a conversation with the developers, but I do need to make my project brief as detailed as possible to receive commensurate proposals.

I don't really have any experience writing a project brief specifically about creating an app, so I'd like to ask you folks what kind of information is important for you to know to help you come up with a good technical and financial proposal for the project.

Please feel free to list down things that might even sound too basic or too obvious for you. Thanks a lot!