Can someone explain the API situation? I have a dev account and I created a project, and I put a credit card in the billing info, and it gave me a maps api key

Can someone explain the API situation? I have a dev account and I created a project, and I put a credit card in the billing info, and it gave me a maps api key which doesn't seem to work in the app (says 'failed to fetch resource). When I go into the project it tried to get me to sign up for a monthly service which was unclear what it does and was not 'escapable' (I had to leave the page or choose a paid plan). I really don't want to hit 'accept' on something and find out a month later I have a bill from google. Is there something simple I am missing?