What is the difference between Trading API and Broker API


I want to build a broker similar to Robinhood. It is a private project that will never be released. Therefore the created accounts should only be able to use paper money.

When I created the Trading API account and tried to login under login it mentions “To integrate stock trading into your app head over to Broker API
I am confused and dont know what to use. I thought I have to create and use the Apps under “OAuth Apps” from the Trading API for my case.
ps: Just out of curiosity I created a Broker API account and there is already a transaction with an amount of $50,000.0. I dont know why