What source information do I need when taking work back from a developer?

Hi everyone,

I hired a freelance developer roughly 1 year ago to develop a mobile app for me. Unfortunately I believe we have hit a wall and he no longer seems to be making progress. I am going to be ending the contract and would like your advice on what I would need from him to enable me to hand this over to a new developer to continue the work?

The app includes payment integration and database storage.

Thanks

Martin